Carrier-bonding methods and articles for semiconductor and interposer processing

ABSTRACT

A thin sheet ( 20 ) disposed on a carrier ( 10 ) via a surface modification layer ( 30 ) to form an article ( 2 ), wherein the article may be subjected to high temperature processing, as in FEOL semiconductor processing, not outgas and have the thin sheet maintained on the carrier without separation therefrom during the processing, yet be separated therefrom upon room temperature peeling force that leaves the thinner one of the thin sheet and carrier intact. Interposers ( 56 ) having arrays ( 50 ) of vias ( 60 ) may be formed on the thin sheet, and devices ( 66 ) formed on the interposers. Alternatively, the thin sheet may be a substrate on which semiconductor circuits are formed during FEOL processing.

This application claims the benefit of priority of U.S. ProvisionalApplication Ser. No. 61/890,524, filed on Oct. 14, 2013, the content ofwhich is relied upon and incorporated herein by reference in itsentirety.

BACKGROUND

1. Field of the Invention

The present invention is generally directed to carriers bonded to andremoved from thinner substrates to allow processing of the thinnersubstrates. More particularly, the present invention is directed tomethods and apparatuses for bonding wafers to carriers for semiconductorand/or interposer processing, and then debonding the wafers from thecarriers after such processing.

2. Technical Background

Semiconductor devices are fabricated by forming active devices on orwithin a semiconductor wafer. The semiconductor wafer may comprise, forexample, glass, silicon, polysilicon, single crystal silicon, siliconoxide, aluminum oxide, combinations of these, and/or the like. Hundredsor thousands of integrated circuits (ICs) or dies are typicallymanufactured on a single wafer. Typically, a plurality of insulating,conductive, and semiconductive material layers are sequentiallydeposited and patterned over the wafer to form the ICs. One of theuppermost-formed material layers typically comprises a layer for bondpads which make electrical connection to the underlying active areas andcomponents within the wafer.

After the ICs are formed, the wafer may be subjected to backsideprocessing. The backside processing may include thinning the wafer toprepare the wafer for packaging. For example, in some technologies,backside processing may include forming electrical connections tothrough-substrate vias formed through the wafer for providing backsidecontacts. In this example, the backside of the wafer is thinned througha process such as grinding in order to expose the conductive vias on thebackside of the wafer. This process of thinning the wafer can damage theedges of the wafer and can make the wafer even more fragile andsusceptible to damage during subsequent transportation and processing ofthe wafer.

To help alleviate these types of damage, a carrier is normally attachedto the wafer. This carrier is attached using an adhesive, and isintended to allow handling of the wafer by handling the carrier.Additionally, the added strength of the carrier supports the wafer sothat stresses caused by transportation and/or processing will not damagethe wafer.

SUMMARY

A typical carrier may be a glass substrate attached to the wafer usingan adhesive. It has been found, however, that the wafer may warp duringprocessing and that the typical carrier does not provide sufficientsupport to prevent warping. As a result of the warpage of the wafer,processes may fail and/or cause alarm conditions. The first portion ofthe IC fabrication, where the active transistors, resistors and RCcircuits, and local wiring to interconnect the transistors are patternedin the semiconductor, is called front-end-of-line (FEOL) processing.FEOL processing may also include: well formation; gate module formation;source and drain module formation; DRIE (dry reactive ion etch); PVD, Tior Cu, or other; CVD TiN or other; PECVD SiO2, or other; Electrolytic Cu(or other) Plating; Cu (or other) annealing; Metrology (X-Ray or other);Cu (or other) CMP (Chemical Mechanical Polish); Cu (H2O2+H2SO4)+Ti (DHF)Wet Etch; Sputter Adhesion Layer (Ti or other); Sputter Seed Layer (Cuor other); Lithography (Photoresist, expose, strip, etch Cu). Due tosome of the high temperature (e.g., ≧500° C., in some instances, 500° C.to 650° C., and in some cases up to 700° C.) processes associated withFEOL processing, many adhesive based solutions cannot be used, as theymay fail to hold the bond, they may outgas contaminants, or both. Manyadhesives even outgas at much lower temperatures, e.g., around 300° C.The portion of IC fabrication line where the coarse wiring that connectslonger distances across individual chip and goes to off chip locationsare interconnected with wiring on the wafer is called back-end-of-line(BEOL) wiring. BEOL processing may also include one or more of formationof contacts, insulating layers, interconnect wiring, RF shielding,passivation, ESD protection, bonding pads and other bonding sites forchip-to-package solutions. Although BEOL processing temperatures aregenerally lower than FEOL processing temperatures, dielectric depositiontypically occurs at 350-450° C. and most adhesives outgas at these lowertemperatures. Moreover, most temporary adhesives have high CTEs whichare mismatched with the wafer and carrier materials, and are difficultto remove while leaving the delicate microstructures on the waferintact. Additionally, the CTE mismatch between the adhesive and thewafer and/or carrier materials may cause undesirable warping of thewafer. Still further, adhesive may find its way into the vias of aninterposer when bonding to a carrier and undesirably preventmetallization of at least part of the via.

Thus, there is a need for an improved carrier-substrate solution thatcan withstand processing conditions, particularly the high temperaturedemands of FEOL processing. Additionally, a carrier-substrate solutionthat can withstand the rigors of FEOL, and yet provide for easydebonding thereafter, will allow a thinner initial substrate to be usedfrom the get-go, thereby alleviating the need for back-end thinning.That is, typical existing semiconductor tools are designed to processwafers on the order of 500 microns and above. However, with a carriersupporting a wafer, the combined thickness need only be within thetools' processing thickness range. Thus, for example, a carrier having athickness of 400 microns may be used to support a wafer of 100 microns,and the combination processed in the existing semiconductor tool. Withthe present solution, due to the controlled bonding that allows easyseparation even after high temperature processing, 100 micron wafers maybe used as substrates, thereby avoiding the waste and potential yieldreductions of thinning after forming devices on the wafer. The abilityto withstand FEOL processing will allow a carrier-substrate solution tostart with a wafer having a thickness of ≦200 microns, for example, 200,190, 180, 170, 160, 150, 140, 130, 120, 110, 100, 90, 80, 70, 60, 50,40, 30, or 20 microns. The wafer of such a thickness (≦200 microns forexample) can be attached to a carrier, processed, and then removed fromthe carrier. This can be a major advantage when, for example,polysilicon or single crystal silicon wafers are used as the substratesbecause there can be avoided the removal and waste of a very expensivematerial; the material can simply be processed at its as-formedthickness.

Additionally, 3D IC technology has been widely accepted by theSemiconductor Industry as a major technology trend to improveperformance of semiconductors without requiring ever more expensiveadvanced lithography solutions or requiring larger chip size toaccommodate more circuitry. This technology for 3D ICs relies on thinnedsilicon ICs, and also on interposers to redistribute electrical signalsbetween IC's directly on a single interposer in a planar configuration(2.5D IC) as well as to stack thinned IC's (3D IC).

These interposers, which can be made of polysilicon, single crystalsilicon or glass, allow dramatic improvements in the speed ofcommunications by reducing path lengths from millimeters to microns. Thelead application for this new technology has been Field ProgrammableGate Arrays (FPGA), a high end specialized functionality manufactured byXilinx (San Jose, Calif., USA), for example.

Interposers are characteristically on the order of 50 um to 100 umthick, sized from 200 mm OD to 300 mm OD today, trending towards largersized panels long term. The vias, through which electrical signals areprocessed following metallization, are from Sum OD to 150 um OD with adensity typically 1 to 20 vias per square millimeter, depending ondesign and application. Interposers are by definition thin, as thickinterposers cause an unacceptable form factor (height) and performance(heat) obstacles. Thin is generally regarded as around 100 microns, butgenerally not to exceed 200 microns. On the other end, the InternationalTechnology Roadmap for Semiconductors (ITRS) allows for thicknesses downto 50 um. Again, substrates of these thicknesses generally cannot beprocessed in existing tools. Thus, the present disclosure contemplatesthe advantageous use of a carrier, and one that may stay attached withthe wafer even during high temperature processing, and yet still allowan easy release of the wafer after such processing.

Although the interposer technology is new, the dominant interposersubstrate is single crystal silicon, with glass emerging as analternative. The attractiveness of glass is performance and cost, but nosolution has yet existed today to realize these advantages for glass.The concepts in the present disclosure will allow processing of avariety of thin substrates as wafers, including silicon and glass, aswell as under a variety of conditions, including FEOL and BEOL, toprovide a variety of devices including ICs, RC circuits, andinterposers.

The bonding solutions of the present disclosure allow the processing ofthin form at final thickness glass, as well as thinned Silicon, throughall existing required process steps with high yield and with lowprocessing time. After the thin wafer is processed throughmetallization, distribution layer placement, it can be debonded leavingthe thinned and processed interposer, and/or IC, intact. Moreover, theuse of carrier with an already-thinned (on the order of ≦200 microns)silicon wafer allows the wafer to be screened before any devices areprocessed thereon. Accordingly, costs can be reduced and/or yieldsimproved.

In light of the above, there is a need for a thin sheet—carrier articlethat can withstand the rigors of the FEOL processing, including hightemperature processing (without outgassing that would be incompatiblewith the semiconductor or display making processes in which it will beused), yet allow the entire area of the thin sheet to be removed (eitherall at once, or in sections) from the carrier. The present specificationdescribes ways to control the adhesion between the carrier and thinsheet to create a temporary bond sufficiently strong to survive FEOLprocessing (including high temperature processing) but weak enough topermit debonding of the sheet from the carrier, even afterhigh-temperature processing. More specifically, the present disclosureprovides surface modification layers (including various materials andassociated surface heat treatments), that may be provided on the thinsheet, the carrier, or both, to control both room-temperature van derWaals, and/or hydrogen, bonding and high temperature covalent bondingbetween the thin sheet and carrier. Even more specifically, theroom-temperature bonding may be controlled so as to be sufficient tohold the thin sheet and carrier together during vacuum processing, wetprocessing, and/or ultrasonic cleaning processing. And at the same time,the high temperature covalent bonding may be controlled so as to preventa permanent bond between the thin sheet and carrier during hightemperature processing, as well as maintain a sufficient bond to preventdelamination during high temperature processing. In alternativeembodiments, the surface modification layers may be used to createvarious controlled bonding areas (wherein the carrier and sheet remainsufficiently bonded through various processes, including vacuumprocessing, wet processing, and/or ultrasonic cleaning processing).Still further, some surface modification layers provide control of thebonding between the carrier and sheet while, at the same time, reduceoutgassing emissions during the harsh conditions in an FPD (for exampleLTPS) processing environment, including high temperature and/or vacuumprocessing, for example.

Additional features and advantages will be set forth in the detaileddescription which follows, and in part will be readily apparent to thoseskilled in the art from the description or recognized by practicing thevarious aspects as exemplified in the written description and theappended drawings. It is to be understood that both the foregoinggeneral description and the following detailed description are merelyexemplary of the various aspects, and are intended to provide anoverview or framework to understanding the nature and character of theinvention as it is claimed.

The accompanying drawings are included to provide a furtherunderstanding of principles of the invention, and are incorporated inand constitute a part of this specification. The drawings illustrate oneor more embodiment(s), and together with the description serve toexplain, by way of example, principles and operation of the invention.It is to be understood that various features disclosed in thisspecification and in the drawings can be used in any and allcombinations. By way of non-limiting example the various features may becombined with one another as set forth in the following aspects:

According to a first aspect, there is provided an article, comprising:

-   -   a carrier with a carrier bonding surface;    -   a sheet with at least one via therein, the sheet further        comprising a sheet bonding surface;    -   a surface modification layer;    -   the carrier bonding surface being bonded with the sheet bonding        surface with the surface modification layer therebetween,        wherein the surface modification layer is of such a character        that after subjecting the article to a temperature cycle by        heating in an chamber cycled from room temperature to 500° C. at        a rate of 9.2° C. per minute, held at a temperature of 500° C.        for 10 minutes, and then cooled at furnace rate to 300° C., and        then removing the article from the chamber and allowing the        article to cool to room temperature, the carrier and sheet do        not separate from one another if one is held and the other        subjected to the force of gravity, and the sheet may be        separated from the carrier without breaking the thinner one of        the carrier and the sheet into two or more pieces when        separation is performed at room temperature.

According to a second aspect, there is provided an article, comprising:

-   -   a carrier with a carrier bonding surface;    -   a sheet with at least one via therein, the sheet further        comprising a sheet bonding surface;    -   a surface modification layer;    -   the carrier bonding surface being bonded with the sheet bonding        surface with the surface modification layer therebetween,        wherein the surface modification layer is of such a character        that after subjecting the article to a temperature cycle by        heating in an chamber cycled from room temperature to 400° C. at        a rate of 9.2° C. per minute, held at a temperature of 400° C.        for 10 minutes, and then cooled at furnace rate to 300° C., and        then removing the article from the chamber and allowing the        article to cool to room temperature, the carrier and sheet do        not separate from one another if one is held and the other        subjected to the force of gravity, there is no outgassing from        the surface modification layer according to test #2, and the        sheet may be separated from the carrier without breaking the        thinner one of the carrier and the sheet into two or more pieces        when separation is performed at room temperature.

According to a third aspect, there is provided the article of aspect 1or aspect 2, the sheet comprises silicon, quartz, sapphire, ceramic, orglass.

According to a fourth aspect, there is provided the article of aspect 1,the sheet thickness is ≦200 microns.

According to a fifth aspect, there is provided an article, comprising:

-   -   a carrier with a carrier bonding surface;    -   a wafer sheet comprising a thickness ≦200 microns, the sheet        further comprising a sheet bonding surface, the sheet comprising        silicon, quartz, or sapphire;    -   a surface modification layer;    -   the carrier bonding surface being bonded with the sheet bonding        surface with the surface modification layer therebetween,        wherein the surface modification layer is of such a character        that after subjecting the article to a temperature cycle by        heating in an chamber cycled from room temperature to 500° C. at        a rate of 9.2° C. per minute, held at a temperature of 500° C.        for 10 minutes, and then cooled at furnace rate to 300° C., and        then removing the article from the chamber and allowing the        article to cool to room temperature, the carrier and sheet do        not separate from one another if one is held and the other        subjected to the force of gravity, and the sheet may be        separated from the carrier without breaking the thinner one of        the carrier and the sheet into two or more pieces when        separation is performed at room temperature.

According to a sixth aspect, there is provided an article, comprising:

-   -   a carrier with a carrier bonding surface;    -   a wafer sheet comprising a thickness ≦200 microns, the sheet        further comprising a sheet bonding surface, the sheet comprising        silicon, quartz, or sapphire;    -   a surface modification layer;    -   the carrier bonding surface being bonded with the sheet bonding        surface with the surface modification layer therebetween,        wherein the surface modification layer is of such a character        that after subjecting the article to a temperature cycle by        heating in an chamber cycled from room temperature to 400° C. at        a rate of 9.2° C. per minute, held at a temperature of 400° C.        for 10 minutes, and then cooled at furnace rate to 300° C., and        then removing the article from the chamber and allowing the        article to cool to room temperature, the carrier and sheet do        not separate from one another if one is held and the other        subjected to the force of gravity, there is no outgassing from        the surface modification layer according to test #2, and the        sheet may be separated from the carrier without breaking the        thinner one of the carrier and the sheet into two or more pieces        when separation is performed at room temperature.

According to a seventh aspect, there is provided the article of aspect 5or aspect 6, the sheet further comprising at least one via therein.

According to an eighth aspect, there is provided the article of any oneof aspects 1-4, 7, the at least one via has a diameter of ≦150 microns.

According to a ninth aspect, there is provided the article of any one ofaspects 1-4, 7, 8, the at least one via comprises electricallyconductive material therein.

According to a tenth aspect, there is provided the article of any one ofaspects 1-9, the sheet comprising a device surface opposite the sheetbonding surface, the device surface comprising an array of devicesselected from the group consisting of: integrated circuits; MEMS; CPU;microsensors; power semiconductors; light-emitting diodes; photoniccircuits; interposers; embedded passive devices; and microdevicesfabricated on or from silicon, silicon-germanium, gallium arsenide, andgallium nitride.

According to an eleventh aspect, there is provided the article of anyone of aspects 1-9, the sheet comprising a device surface opposite thesheet bonding surface, the device surface comprising at least onestructure selected from the group consisting of: solder bumps; metalposts; metal pillars; interconnection routings; interconnect lines;insulating oxide layers; and structures formed from a material selectedfrom the group consisting of silicon, polysilicon, silicon dioxide,silicon (oxy)nitride, metal, low k dielectrics, polymer dielectrics,metal nitrides, and metal silicides.

According to a twelfth aspect, there is provided the article of any oneof aspects 1-11, wherein the heating is performed in Nitrogen.

According to a thirteenth aspect, there is provided the article of anyone of aspects 1, 3-5, 7-12, wherein there is no outgassing from thesurface modification layer during the heating, wherein outgassing fromthe surface modification layer is defined as at least one of:

-   -   (a) wherein the change in surface energy of the cover is ≧15        mJ/m² at a test-limit temperature of 600° C. according to        outgassing test #1; and    -   (b) wherein the change in % bubble area is ≧5 at a test limit        temperature of 600° C. according to outgassing test #2.

According to a fourteenth aspect, there is provided the article of anyone of aspects 1-13, the surface modification layer comprises one of:

-   -   a) a plasma polymerized fluoropolymer; and    -   b) an aromatic silane.

According to a fifteenth aspect, there is provided the article of anyone of aspects 1-14, thickness of the surface modification layer is from0.1 to 100 nm.

According to a sixteenth aspect, there is provided the article of anyone of aspects 1-15, the carrier comprises glass.

According to a seventeenth aspect, there is provided the article of anyone of aspects 1-16, wherein the bonding surface of at least one of thecarrier and the sheet comprises an area of ≧100 square cm.

According to an eighteenth aspect, there is provided a method of makingan interposer, comprising:

-   -   obtaining a carrier with a carrier bonding surface;    -   obtaining a sheet with at least one via therein, the sheet        further comprising a sheet bonding surface, wherein at least one        of the carrier bonding surface and the sheet bonding surface        comprises a surface modification layer thereon;    -   bonding the carrier to the sheet with the bonding surfaces and        the surface modification layer to form an article;    -   subjecting the article to front-end-of-line (FEOL) processing,        wherein after FEOL processing the carrier and sheet do not        separate from one another if one is held and the other subjected        to the force of gravity;    -   removing the sheet from the carrier without breaking the thinner        one of the carrier and the sheet into two or more pieces.

According to a ninteenth aspect, there is provided the method of aspect18, the sheet comprises silicon, quartz, sapphire, ceramic, or glass.

According to a twentieth aspect, there is provided the method of aspect18, the sheet thickness is ≦200 microns.

According to a twenty first aspect, there is provided a method ofprocessing a silicon wafer sheet, comprising:

-   -   obtaining a carrier with a carrier bonding surface;    -   obtaining a wafer sheet with a thickness ≦200 microns, the sheet        comprising silicon, quartz, or sapphire, the sheet further        comprising a sheet bonding surface, wherein at least one of the        carrier bonding surface and the sheet bonding surface comprises        a surface modification layer thereon;    -   bonding the carrier to the sheet with the bonding surfaces and        the surface modification layer to form an article;    -   subjecting the article to front-end-of-line (FEOL) processing,        wherein after FEOL processing the carrier and sheet do not        separate from one another if one is held and the other subjected        to the force of gravity;    -   removing the sheet from the carrier without breaking the thinner        one of the carrier and the sheet into two or more pieces.

According to a twenty second aspect, there is provided the method ofaspect 21, the sheet further comprising at least one via therein.

According to a twenty third aspect, there is provided the method of anyone of aspects 18-22, wherein the FEOL processing comprisesprocessing-chamber temperatures of from 500° C. to 700° C.

According to a twenty fourth aspect, there is provided the method of anyone of aspects 18-22, wherein the FEOL processing comprises at least oneof: DRIE (dry reactive ion etch); PVD; CVD TiN; PECVD SiO2; ElectrolyticCu Plating; Cu Annealing; Metrology; Cu CMP; Cu (H2O2+H2SO4)+Ti (DHF)Wet Etch; Sputter Adhesion Layer; Sputter Seed Layer; Lithography(Photoresist, expose, strip, etch Cu).

According to a twenty fifth aspect, there is provided the method of anyone of aspects 18-20, 22-24, the at least one via has a diameter of ≦150microns.

According to a twenty sixth aspect, there is provided the method of anyone of aspects 18-20, 22-25, the at least one via comprises electricallyconductive material therein.

According to a twenty seventh aspect, there is provided the method ofany one of aspects 18-26, the sheet comprising a device surface oppositethe sheet bonding surface, the device surface comprising an array ofdevices selected from the group consisting of: integrated circuits;MEMS; CPU; microsensors; power semiconductors; light-emitting diodes;photonic circuits; interposers; embedded passive devices; andmicrodevices fabricated on or from silicon, silicon-germanium, galliumarsenide, and gallium nitride.

According to a twenty eighth aspect, there is provided the method of anyone of aspects 18-26, the sheet comprising a device surface opposite thesheet bonding surface, the device surface comprising at least onestructure selected from the group consisting of: solder bumps; metalposts; metal pillars; interconnection routings; interconnect lines;insulating oxide layers; and structures formed from a material selectedfrom the group consisting of silicon, polysilicon, silicon dioxide,silicon (oxy)nitride, metal, low k dielectrics, polymer dielectrics,metal nitrides, and metal silicides.

According to a twenty ninth aspect, there is provided the method of anyone of aspects 18-28, wherein the heating is performed in Nitrogen.

According to a thirtieth aspect, there is provided the method of any oneof aspects 18-29, wherein there is no outgassing from the surfacemodification layer during the heating, wherein outgassing from thesurface modification layer is defined as at least one of:

-   -   (a) wherein the change in surface energy of the cover is ≧15        mJ/m² at a test-limit temperature of 600° C. according to        outgassing test #1; and    -   (b) wherein the change in % bubble area is ≧5 at a test limit        temperature of 600° C. according to outgassing test #2.

According to a thirty first aspect, there is provided the method of anyone of aspects 18-30, the surface modification layer comprises one of:

-   -   a) a plasma polymerized fluoropolymer; and    -   b) an aromatic silane.

According to a thirty second aspect, there is provided the method of anyone of aspects 18-31, thickness of the surface modification layer isfrom 0.1 to 100 nm.

According to a thirty third aspect, there is provided the method of anyone of aspects 18-32, the carrier comprises glass.

According to a thirty fourth aspect, there is provided the method of anyone of aspects 18-33, wherein the bonding surface of at least one of thecarrier and the sheet comprises an area of ≧100 square cm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an article having carrier bonded to athin sheet with a surface modification layer therebetween.

FIG. 2 is an exploded and partially cut-away view of the article in FIG.1.

FIG. 3 is a graph of surface hydroxyl concentration on silica as afunction of temperature.

FIG. 4 is a graph of the surface energy of an SC1-cleaned sheet of glassas a function annealing temperature.

FIG. 5 is a graph of the surface energy of a thin fluoropolymer filmdeposited on a sheet of glass as a function of the percentage of one ofthe constituent materials from which the film was made.

FIG. 6 is a schematic view of a testing setup

FIG. 7 is a collection of graphs of surface energy (of different partsof the test setup of FIG. 6) versus time for a variety of materialsunder different conditions.

FIG. 8 is a graph of change in % bubble area versus temperature for avariety of materials.

FIG. 9 is another graph of change in % bubble area versus temperaturefor a variety of materials.

FIG. 10 is a top view of a thin sheet and carrier, having interposers.

FIG. 11 is a cross-sectional view of the thin sheet and carrier as takenalong line 11-11 of FIG. 10.

FIG. 12 is a cross-sectional view, similar to that in FIG. 11, buthaving additional devices disposed on the thin sheet.

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation andnot limitation, example embodiments disclosing specific details are setforth to provide a thorough understanding of various principles of thepresent invention. However, it will be apparent to one having ordinaryskill in the art, having had the benefit of the present disclosure, thatthe present invention may be practiced in other embodiments that departfrom the specific details disclosed herein. Moreover, descriptions ofwell-known devices, methods and materials may be omitted so as not toobscure the description of various principles of the present invention.Finally, wherever applicable, like reference numerals refer to likeelements.

Ranges can be expressed herein as from “about” one particular value,and/or to “about” another particular value. When such a range isexpressed, another embodiment includes from the one particular valueand/or to the other particular value. Similarly, when values areexpressed as approximations, by use of the antecedent “about,” it willbe understood that the particular value forms another embodiment. Itwill be further understood that the endpoints of each of the ranges aresignificant both in relation to the other endpoint, and independently ofthe other endpoint.

Directional terms as used herein—for example up, down, right, left,front, back, top, bottom—are made only with reference to the figures asdrawn and are not intended to imply absolute orientation.

Unless otherwise expressly stated, it is in no way intended that anymethod set forth herein be construed as requiring that its steps beperformed in a specific order. Accordingly, where a method claim doesnot actually recite an order to be followed by its steps or it is nototherwise specifically stated in the claims or descriptions that thesteps are to be limited to a specific order, it is no way intended thatan order be inferred, in any respect. This holds for any possiblenon-express basis for interpretation, including: matters of logic withrespect to arrangement of steps or operational flow; plain meaningderived from grammatical organization or punctuation; the number or typeof embodiments described in the specification.

As used herein, the singular forms “a,” “an” and “the” include pluralreferents unless the context clearly dictates otherwise. Thus, forexample, reference to a “component” includes aspects having two or moresuch components, unless the context clearly indicates otherwise.

It is desirable to be able to remove the thin sheet, or portionsthereof, from the carrier to process more than one thin sheet substrate.The present disclosure sets forth articles and methods for enabling athin sheet to be processed through high temperature processing—whereinhigh temperature processing is processing at a temperature ≧400° C., andmay vary depending upon the type of device being made, for example,temperatures up to about 450° C. as in amorphous silicon or amorphousindium gallium zinc oxide (IGZO) backplane processing, up to about500-550° C. as in crystalline IGZO processing, or up to about 600-650°C. as is typical in LTPS processes—and yet still allows the thin sheetto be easily removed from the carrier without damage (for example,wherein one of the carrier and the thin sheet breaks or cracks into twoor more pieces) to the thin sheet or carrier. Although specificprocesses are mentioned, they are merely exemplary of processes havingcertain temperature requirements. Of course, if a thin sheet and carriermay be used in any one of the above processes, it may be used in adifferent process having a similar temperature requirement.

As shown in FIGS. 1 and 2, an article 2 has a thickness 8, and includesa carrier 10 having a thickness 18, a thin sheet 20 (i.e., one having athickness of ≦300 microns, including but not limited to thicknesses of,for example, 10-50 microns, 50-100 microns, 100-150 microns, 150-300microns, 300, 250, 200 190, 180, 170, 160, 150 140, 130, 120 110 100,90, 80, 70, 60, 50, 40 30, 20, or 10, microns) having a thickness 28,and a surface modification layer 30 having a thickness 38. The article 2is designed to allow the processing of thin sheet 20 in equipmentdesigned for thicker sheets (i.e., those on the order of ≧0.4 mm, e.g.,0.4 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, or 1.0 mm) although thethin sheet 20 itself is ≦300 microns. That is, the thickness 8, which isthe sum of thicknesses 18, 28, and 38, is designed to be equivalent tothat of the thicker sheet for which a piece of equipment—for example,equipment designed to dispose electronic device components ontosubstrate sheets—was designed to process. For example, if the processingequipment was designed for a 700 micron sheet, and the thin sheet had athickness 28 of 300 microns, then thickness 18 would be selected as 400microns, assuming that thickness 38 is negligible. That is, the surfacemodification layer 30 is not shown to scale; instead, it is greatlyexaggerated for sake of illustration only. Additionally, the surfacemodification layer is shown in cut-away. In actuality, the surfacemodification layer would be disposed uniformly over the bonding surface14. Typically, thickness 38 will be on the order of nanometers, forexample 0.1 to 2.0, or up to 10 nm, and in some instances may be up to100 nm. The thickness 38 may be measured by ellipsometer. Additionally,the presence of a surface modification layer may be detected by surfacechemistry analysis, for example by ToF Sims mass spectrometry.Accordingly, the contribution of thickness 38 to the article thickness 8is negligible and may be ignored in the calculation for determining asuitable thickness 18 of carrier 10 for processing a given thin sheet 20having a thickness 28. However, to the extent that surface modificationlayer 30 has any significant thickness 38, such may be accounted for indetermining the thickness 18 of a carrier 10 for a given thickness 28 ofthin sheet 20, and a given thickness for which the processing equipmentwas designed.

Carrier 10 has a first surface 12, a bonding surface 14, a perimeter 16,and thickness 18. Further, the carrier 10 may be of any suitablematerial including glass, for example. The carrier need not be glass,but instead can be ceramic, glass-ceramic, or metal (as the surfaceenergy and/or bonding may be controlled in a manner similar to thatdescribed below in connection with a glass carrier). If made of glass,carrier 10 may be of any suitable composition includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali-freedepending upon its ultimate application. Thickness 18 may be from about0.2 to 3 mm, or greater, for example 0.2, 0.3, 0.4, 0.5, 0.6, 0.65, 0.7,1.0, 2.0, or 3 mm, or greater, and will depend upon the thickness 28,and thickness 38 when such is non-negligible, as noted above.Additionally, the carrier 10 may be made of one layer, as shown, ormultiple layers (including multiple thin sheets) that are bondedtogether. Further, the carrier may be of a Gen 1 size or larger, forexample, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 or larger (e.g., sheet sizesfrom 100 mm×100 mm to 3 meters×3 meters or greater).

The thin sheet 20 has a first surface 22, a bonding surface 24, aperimeter 26, and thickness 28. Perimeters 16 and 26 may be of anysuitable shape, may be the same as one another, or may be different fromone another. Further, the thin sheet 20 may be of any suitable materialincluding silicon, polysilicon, single crystal silicon, sapphire,quartz, glass, ceramic, or glass-ceramic, for example. When made ofglass, thin sheet 20 may be of any suitable composition, includingalumino-silicate, boro-silicate, alumino-boro-silicate,soda-lime-silicate, and may be either alkali containing or alkali freedepending upon its ultimate application. The coefficient of thermalexpansion of the thin sheet could be matched relatively closely withthat of the carrier to prevent warping of the article during processingat elevated temperatures. The thickness 28 of the thin sheet 20 is 300microns or less, as noted above. Further, the thin sheet may be of a Gen1 size or larger, for example, Gen 2, Gen 3, Gen 4, Gen 5, Gen 8 orlarger (e.g., sheet sizes from 100 mm×100 mm to 3 meters×3 meters orgreater).

Not only does the article 2 need to have the correct thickness to beprocessed in the existing equipment, it will also need to be able tosurvive the harsh environment in which the processing takes place. Forexample, processing may include wet ultrasonic, vacuum, and hightemperature (e.g., ≧400° C.), processing. For some processes, as notedabove, the temperature may be ≧500° C., or ≧600° C., and up to 650° C.

In order to survive the harsh environment in which article 2 will beprocessed, the bonding surface 14 should be bonded to bonding surface 24with sufficient strength so that the thin sheet 20 does not separatefrom carrier 10. And this strength should be maintained through theprocessing so that the thin sheet 20 does not separate from the carrier10 during processing. Further, to allow the thin sheet 20 to be removedfrom carrier 10 (so that carrier 10 may be reused), the bonding surface14 should not be bonded to bonding surface 24 too strongly either by theinitially designed bonding force, and/or by a bonding force that resultsfrom a modification of the initially designed bonding force as mayoccur, for example, when the article undergoes processing at hightemperatures, e.g., temperatures of ≧400° C. The surface modificationlayer 30 may be used to control the strength of bonding between bondingsurface 14 and bonding surface 24 so as to achieve both of theseobjectives. The controlled bonding force is achieved by controlling thecontributions of van der Waals (and/or hydrogen bonding) and covalentattractive energies to the total adhesion energy which is controlled bymodulating the polar and non-polar surface energy components of the thinsheet 20 and the carrier 10. This controlled bonding is strong enough tosurvive processing (including wet, ultrasonic, vacuum, and thermalprocesses including temperatures ≧400° C., and in some instances,processing temperatures of ≧500° C., or ≧600° C., and up to 650° C.) andremain de-bondable by application of sufficient separation force and yetby a force that will not cause catastrophic damage to the thin sheet 20and/or the carrier 10. Such de-bonding permits removal of thin sheet 20and the devices fabricated thereon, and also allows for re-use of thecarrier 10.

Although the surface modification layer 30 is shown as a solid layerbetween thin sheet 20 and carrier 10, such need not be the case. Forexample, the layer 30 may be on the order of 0.1 to 2 nm thick, and maynot completely cover every bit of the bonding surface 14. For example,the coverage may be ≦100%, from 1% to 100%, from 10% to 100%, from 20%to 90%, or from 50% to 90%. In other embodiments, the layer 30 may be upto 10 nm thick, or in other embodiments even up to 100 nm thick. Thesurface modification layer 30 may be considered to be disposed betweenthe carrier 10 and thin sheet 20 even though it may not contact one orthe other of the carrier 10 and thin sheet 20. In any event, animportant aspect of the surface modification layer 30 is that itmodifies the ability of the bonding surface 14 to bond with bondingsurface 24, thereby controlling the strength of the bond between thecarrier 10 and the thin sheet 20. The material and thickness of thesurface modification layer 30, as well as the treatment of the bondingsurfaces 14, 24 prior to bonding, can be used to control the strength ofthe bond (energy of adhesion) between carrier 10 and thin sheet 20.

In general, the energy of adhesion between two surfaces is given by (“Atheory for the estimation of surface and interfacial energies. I.derivation and application to interfacial tension”, L. A. Girifalco andR. J. Good, J. Phys. Chem., V 61, p904):

W=γ ₁+γ₂−γ₁₂  (1)

where ,γ₁, γ₂ and γ₁₂ are the surface energies of surface 1, surface 2and the interfacial energy of surface 1 and 2 respectively. Theindividual surface energies are usually a combination of two terms; adispersion component γ^(d), and a polar component γ^(p)

γ=γ^(d)+γ^(p)  (2)

When the adhesion is mostly due to London dispersion forces (γ^(d)) andpolar forces for example hydrogen bonding (γ^(p)), the interfacialenergy could be given by (Girifalco and R. J. Good, as mentioned above):

γ₁₂=γ₁+γ₂−2√{square root over (γ₁ ^(d)γ₂ ^(d))}−2√{square root over (γ₁^(p)γ₂ ^(p))}  (3)

After substituting (3) in (1), the energy of adhesion could beapproximately calculated as:

W˜2┌√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}┐  (4)

In the above equation (4), only van der Waal (and/or hydrogen bonding)components of adhesion energies are considered. These includepolar-polar interaction (Keesom), polar-non polar interaction (Debye)and nonpolar-nonpolar interaction (London). However, other attractiveenergies may also be present, for example covalent bonding andelectrostatic bonding. So, in a more generalized form, the aboveequation is written as:

W˜2[√{square root over (γ₁ ^(d)γ₂ ^(d))}+√{square root over (γ₁ ^(p)γ₂^(p))}]+w _(c) +w _(e)  (5)

where w_(c) and w_(e) are the covalent and electrostatic adhesionenergies. The covalent adhesion energy is rather common, as in siliconwafer bonding where an initially hydrogen bonded pair of wafers areheated to a higher temperature to convert much or all thesilanol-silanol hydrogen bonds to Si—O—Si covalent bonds. While theinitial, room temperature, hydrogen bonding produces an adhesion energyof the order of ˜100-200 mJ/m² which allows separation of the bondedsurfaces, a fully covalently bonded wafer pair as achieved during hightemperature processing (on the order of 400 to 800° C.) has adhesionenergy of 1000-3000 mJ/m² which does not allow separation of the bondedsurfaces; instead, the two wafers act as a monolith. On the other hand,if both the surfaces are perfectly coated with a low surface energymaterial, for example a fluoropolymer, with thickness large enough toshield the effect of the underlying substrate, the adhesion energy wouldbe that of the coating material, and would be very low leading to low orno adhesion between the bonding surfaces 14, 24, whereby the thin sheet20 would not be able to be processed on carrier 10. Consider two extremecases: (a) two standard clean 1 (SC1, as known in the art) cleaned glasssurfaces saturated with silanol groups bonded together at roomtemperature via hydrogen bonding (whereby the adhesion energy is˜100-200 mJ/m²) followed by heating to high temperature which convertsthe silanol groups to covalent Si—O—Si bonds (whereby the adhesionenergy becomes 1000-3000 mJ/m²). This latter adhesion energy is too highfor the pair of glass surfaces to be detachable; and (b) two glasssurfaces perfectly coated with a fluoropolymer with low surface adhesionenergy (˜12 mJ/m² per surface) bonded at room temperature and heated tohigh temperature. In this latter case (b), not only do the surfaces notbond (because the total adhesion energy of ˜24 mJ/m², when the surfacesare put together, is too low), they do not bond at high temperatureeither as there are no (or too few) polar reacting groups Between thesetwo extremes, a range of adhesion energies exist, for example between50-1000 mJ/m², which can produce the desired degree of controlledbonding. Accordingly, the inventors have found various manners ofproviding a surface modification layer 30 leading to an adhesion energythat is between these two extremes, and such that there can be produceda controlled bonding that is sufficient enough to maintain a pair ofsubstrates (for example a carrier 10 and a thin sheet 20) bonded to oneanother through the rigors of FPD processing but also of a degree that(even after high temperature processing of, e.g. ≧400° C.) allows thedetachment of the thin sheet 20 from the carrier 10 after processing iscomplete. Moreover, the detachment of the thin sheet 20 from the carrier10 can be performed by mechanical forces, and in such a manner thatthere is no catastrophic damage to at least the thin sheet 20, andpreferably also so that there is no catastrophic damage to the carrier10.

Equation (5) describes that the adhesion energy is a function of foursurface energy parameters plus the covalent and electrostatic energy, ifany.

An appropriate adhesion energy can be achieved by judicious choice ofsurface modifiers, i.e., of surface modification layer 30, and/orthermal treatment of the surfaces prior to bonding. The appropriateadhesion energy may be attained by the choice of chemical modifiers ofeither one or both of bonding surface 14 and bonding surface 24, whichin turn control both the van der Waal (and/or hydrogen bonding, as theseterms are used interchangeably throughout the specification) adhesionenergy as well as the likely covalent bonding adhesion energy resultingfrom high temperature processing (e.g., on the order of ≧400° C.). Forexample, taking a bonding surface of SC1 cleaned glass (that isinitially saturated with silanol groups with high polar component ofsurface energy), and coating it with a low energy fluoropolymer providesa control of the fractional coverage of the surface by polar andnon-polar groups. This not only offers control of the initial van derWaals (and/or hydrogen) bonding at room temperature, but also providescontrol of the extent/degree of covalent bonding at higher temperature.Control of the initial van der Waals (and/or hydrogen) bonding at roomtemperature is performed so as to provide a bond of one surface to theother to allow vacuum and or spin-rinse-dry (SRD) type processing, andin some instances also an easily formed bond of one surface to theother—wherein the easily formed bond can be performed at roomtemperature without application of externally applied forces over theentire area of the thin sheet 20 as is done in pressing the thin sheet20 to the carrier 10 with a squeegee, or with a reduced pressureenvironment. That is, the initial van der Waals bonding provides atleast a minimum degree of bonding holding the thin sheet and carriertogether so that they do not separate if one is held and the other isallowed to be subjected to the force of gravity. In most cases, theinitial van der Walls (and/or hydrogen) bonding will be of such anextent that the article may also go through vacuum, SRD, and ultrasonicprocessing without the thin sheet delaminating from the carrier. Thisprecise control of both van der Waal (and/or hydrogen bonding) andcovalent interactions at appropriate levels via surface modificationlayer 30 (including the materials from which it is made and/or thesurface treatment of the surface to which it is applied), and/or by heattreatment of the bonding surfaces prior to bonding them together,achieves the desired adhesion energy that allows thin sheet 20 to bondwith carrier 10 throughout FPD style processing, while at the same time,allowing the thin sheet 20 to be separated (by an appropriate forceavoiding damage to the thin sheet 20 and/or carrier) from the carrier 10after FPD style processing. In addition, in appropriate circumstances,electrostatic charge could be applied to one or both glass surfaces toprovide another level of control of the adhesion energy.

High temperature processing, FPD processing for example p-Si and oxideTFT fabrication, typically involve thermal processes at temperaturesabove 400° C., above 500° C., and in some instances at or above 600° C.,up to 650° C. which would cause glass to glass bonding of a thin sheet20 with a carrier 10 in the absence of surface modification layer 30.Therefore controlling the formation of Si—O—Si bonding leads to areusable carrier. One method of controlling the formation of Si—O—Sibonding at elevated temperature is to reduce the concentration ofsurface hydroxyls on the surfaces to be bonded.

As shown in FIG. 3, which is Iler's plot (R. K. Iller: The Chemistry ofSilica (Wiley-Interscience, New York, 1979) of surface hydroxylconcentration on silica as a function of temperature, the number ofhydroxyls (OH groups) per square nm decreases as the temperature of thesurface increases. Thus, heating a silica surface (and by analogy aglass surface, for example bonding surface 14 and/or bonding surface 24)reduces the concentration of surface hydroxyls, decreasing theprobability that hydroxyls on two glass surfaces will interact. Thisreduction of surface hydroxyl concentration in turn reduces the Si—O—Sibonds formed per unit area, lowering the adhesive force. However,eliminating surface hydroxyls requires long annealing times at hightemperatures (above 750° C. to completely eliminate surface hydroxyls).Such long annealing times and high annealing temperatures result in anexpensive process, and one which is not practical as it is likely to beabove the strain point of typical display glass.

From the above analysis, the inventors have found that an articleincluding a thin sheet and a carrier, suitable for high temperature, forexample, FPD processing (including LTPS processing), can be made bybalancing the following three concepts:

(1) Modification of the carrier and/or thin sheet bonding surface(s), bycontrolling initial room temperature bonding, which can be done bycontrolling van der Waals (and/or hydrogen) bonding, to create amoderate adhesion energy (for example, having a surface energy of ≧40mJ/m² per surface prior to the surfaces being bonded) to facilitateinitial room temperature bonding, and sufficient to survivenon-high-temperature FPD processes, for example, vacuum processing, SRDprocessing, and/or ultrasonic processing;

(2) Surface modification of a carrier and/or a thin sheet in a mannerthat is thermally stable to survive high temperature processes withoutoutgassing which can cause delamination and/or unacceptablecontamination in the device fabrication, for example, contaminationunacceptable to the semiconductor and/or display making processes inwhich the article may be used; and

(3) Controlling bonding at high temperatures, which can be done bycontrolling the carrier surface hydroxyl concentration, andconcentration of other species capable of forming strong covalent bondsat elevated temperatures (e.g., temperature ≧400° C.), whereby there canbe controlled the bonding energy between the bonding surfaces of thecarrier and the thin sheet such that even after high temperatureprocessing (especially through thermal processes in the range of500-650° C.) the adhesive force between the carrier and thin sheetremains within a range that allows debonding of the thin sheet from thecarrier with a separation force that does not damage at least the thinsheet (and preferably that does not damage either the thin sheet or thecarrier), and yet sufficient enough to maintain the bond between thecarrier and thin sheet so that they do not delaminate during processing.

Further, the inventors have found that the use of a surface modificationlayer 30, together with bonding surface preparation as appropriate, canbalance the above concepts so as readily to achieve a controlled bondingarea, that is, a bonding area that provides a sufficientroom-temperature bond between the thin sheet 20 and carrier 10 to allowthe article 2 to be processed in FPD type processes (including vacuumand wet processes), and yet one that controls covalent bonding betweenthe thin sheet 20 and carrier 10 (even at elevated temperatures ≧400°C.) so as to allow the thin sheet 20 to be removed from the carrier 10(without damage to at least the thin sheet, and preferably withoutdamage to the carrier also) after the article 2 has finished hightemperature processing, for example, FPD type processing or LTPSprocessing. To evaluate potential bonding surface preparations, andsurface modification layers, that would provide for full separation ofthe thin sheet from the carrier, suitable for high temperatureprocessing, a series of tests were used to evaluate the suitability ofeach. Different FPD applications have different requirements, but LTPSand Oxide TFT processes appear to be the most stringent at this timeand, thus, tests representative of steps in these processes were chosen,as these are desired applications for the article 2. Vacuum processes,wet cleaning (including SRD and ultrasonic type processes) and wetetching are common to many FPD applications. Typical aSi TFT fabricationrequires processing up to 320° C. Annealing at 400° C. is used in oxideTFT processes, whereas crystallization and dopant activation steps over600° C. are used in LTPS processing. Accordingly, the following fivetests were used to evaluate the likelihood that a particular bondingsurface preparation and surface modification layer 30 would allow a thinsheet 20 to remain bonded to a carrier 10 throughout FPD processing,while allowing the thin sheet 20 to be removed from the carrier 10(without damaging the thin sheet 20 and/or the carrier 10) after suchprocessing (including processing at temperatures ≧400° C.). The testswere performed in order, and a sample progressed from one test to thenext unless there was failure of the type that would not permit thesubsequent testing.

(1) Vacuum testing. Vacuum compatibility testing was performed in an STSMultiplex PECVD loadlock (available from SPTS, Newport, UK)—The loadlockwas pumped by an Ebara A10S dry pump with a soft pump valve (availablefrom Ebara Technologies Inc., Sacramento, Calif. A sample was placed inthe loadlock, and then the loadlock was pumped from atmospheric pressuredown to 70 mTorr in 45 sec. Failure, indicated by a notation of “F” inthe “Vacuum” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier). In the tablesbelow, a notation of “P” in the “Vacuum” column indicates that thesample did not fail as per the foregoing criteria.

(2) Wet process testing. Wet processes compatibility testing wasperformed using a Semitool model SRD-470S (available from AppliedMaterials, Santa Clara, Calif.). The testing consisted of 60 seconds 500rpm rinse, Q-rinse to 15 MOhm-cm at 500 rpm, 10 seconds purge at 500rpm, 90 seconds dry at 1800 rpm, and 180 seconds dry at 2400 rpm underwarm flowing nitrogen. Failure, as indicated by a notation of “F” in the“SRD” column of the tables below, was deemed to have occurred if therewas: (a) a loss of adhesion between the carrier and the thin sheet (byvisual inspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) movement ofthe thin sheet relative to the carrier (as determined by visualobservation with the naked eye—samples were photographed before andafter testing, wherein failure was deemed to have occurred if there wasa movement of bond defects, e.g., bubbles, or if edges debonded, or ifthere was a movement of the thin sheet on the carrier); or (d)penetration of water under the thin sheet (as determined by visualinspection with an optical microscope at 50×, wherein failure wasdetermined to have occurred if liquid or residue was observable). In thetables below, a notation of “P” in the “SRD” column indicates that thesample did not fail as per the foregoing criteria.

(3) Temperature to 400° C. testing. 400° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP (available fromAlwin21, Santa Clara Calif. A carrier with a thin sheet bonded theretowas heated in a chamber cycled from room temperature to 400° C. at 6.2°C./min, held at 400° C. for 600 seconds, and cooled at 1° C./min to 300°C. The carrier and thin sheet were then allowed to cool to roomtemperature. Failure, as indicated by a notation of “F” in the “400° C.”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape, 1″wide×6″ long with 2-3″ attached to 100 mm square thin glass (K102 seriesfrom Saint Gobain Performance Plastic, Hoosik N.Y.) to the thin sheetand pulling on the tape) of the thin sheet from the carrier withoutdamaging the thin sheet or the carrier, wherein a failure was deemed tohave occurred if there was damage to the thin sheet or carrier uponattempting to separate them, or if the thin sheet and carrier could notbe debonded by performance of either of the debonding methods.Additionally, after the thin sheet was bonded with the carrier, andprior to the thermal cycling, debonding tests were performed onrepresentative samples to determine that a particular material,including any associated surface treatment, did allow for debonding ofthe thin sheet from the carrier prior to the temperature cycling. In thetables below, a notation of “P” in the “400° C.” column indicates thatthe sample did not fail as per the foregoing criteria.

(4) Temperature to 600° C. testing. 600° C. process compatibilitytesting was performed using an Alwin21 Accuthermo610 RTP. A carrier witha thin sheet was heated in a chamber cycled from room temperature to600° C. at 9.5° C./min, held at 600° C. for 600 seconds, and then cooledat 1° C./min to 300° C. The carrier and thin sheet were then allowed tocool to room temperature. Failure, as indicated by a notation of “F” inthe “600° C.” column of the tables below, was deemed to have occurred ifthere was: (a) a loss of adhesion between the carrier and the thin sheet(by visual inspection with the naked eye, wherein failure was deemed tohave occurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) increasedadhesion between the carrier and the thin sheet whereby such increasedadhesion prevents debonding (by insertion of a razor blade between thethin sheet and carrier, and/or by sticking a piece of Kapton™ tape asdescribed above to the thin sheet and pulling on the tape) of the thinsheet from the carrier without damaging the thin sheet or the carrier,wherein a failure was deemed to have occurred if there was damage to thethin sheet or carrier upon attempting to separate them, or if the thinsheet and carrier could not be debonded by performance of either of thedebonding methods. Additionally, after the thin sheet was bonded withthe carrier, and prior to the thermal cycling, debonding tests wereperformed on representative samples to determine that a particularmaterial, and any associated surface treatment, did allow for debondingof the thin sheet from the carrier prior to the temperature cycling. Inthe tables below, a notation of “P” in the “600° C.” column indicatesthat the sample did not fail as per the foregoing criteria.

(5) Ultrasonic testing. Ultrasonic compatibility testing was performedby cleaning the article in a four tank line, wherein the article wasprocessed in each of the tanks sequentially from tank #1 to tank #4.Tank dimensions, for each of the four tanks, were 18.4″L×10″W×15″D. Twocleaning tanks (#1 and #2) contained 1% Semiclean KG available fromYokohama Oils and Fats Industry Co Ltd., Yokohama Japan in DI water at50° C. The cleaning tank #1 was agitated with a NEY prosonik 2 104 kHzultrasonic generator (available from Blackstone-NEY Ultrasonics,Jamestown, N.Y.), and the cleaning tank #2 was agitated with a NEYprosonik 2 104 kHz ultrasonic generator. Two rinse tanks (tank #3 andtank #4) contained DI water at 50° C. The rinse tank #3 was agitated byNEY sweepsonik 2D 72 kHz ultrasonic generator and the rinse tank #4 wasagitated by a NEY sweepsonik 2D 104 kHz ultrasonic generator. Theprocesses were carried out for 10 min in each of the tanks #1-4,followed by spin rinse drying (SRD) after the sample was removed fromtank #4. Failure, as indicated by a notation of “F” in the ““Ultrasonic”column of the tables below, was deemed to have occurred if there was:(a) a loss of adhesion between the carrier and the thin sheet (by visualinspection with the naked eye, wherein failure was deemed to haveoccurred if the thin sheet had fallen off of the carrier or waspartially debonded therefrom); (b) bubbling between the carrier and thethin sheet (as determined by visual inspection with the nakedeye—samples were photographed before and after the processing, and thencompared, failure was determined to have occurred if defects increasedin size by dimensions visible to the unaided eye); or (c) formation ofother gross defects (as determined by visual inspection with opticalmicroscope at 50×, wherein failure was deemed to have occurred if therewere particles trapped between the thin sheet and carrier that were notobserved before; or (d) penetration of water under the thin sheet (asdetermined by visual inspection with an optical microscope at 50×,wherein failure was determined to have occurred if liquid or residue wasobservable. In the tables below, a notation of “P” in the “Ultrasonic”column indicates that the sample did not fail as per the foregoingcriteria. Additionally, in the tables below, a blank in the “Ultrasonic”column indicates that the sample was not tested in this manner.

Preparation of Bonding Surfaces via Hydroxyl Reduction by Heating

The benefit of modifying one or more of the bonding surfaces 14, 24 witha surface modification layer 30 so the article 2 is capable ofsuccessfully undergoing FPD processing (i.e., where the thin sheet 20remains bonded to the carrier 10 during processing, and yet may beseparated from the carrier 10 after processing, including hightemperature processing) was demonstrated by processing articles 2 havingcarriers 10 and thin sheets 20 without a surface modification layer 30therebetween. Specifically, first there was tried preparation of thebonding surfaces 14, 24 by heating to reduce hydroxyl groups, butwithout a surface modification layer 30. The carriers 10 and thin sheets20 were cleaned, the bonding surfaces 14 and 24 were bonded to oneanother, and then the articles 2 were tested. A typical cleaning processfor preparing glass for bonding is the SC1 cleaning process where theglass is cleaned in a dilute hydrogen peroxide and base (commonlyammonium hydroxide, but tetramethylammonium hydroxide solutions forexample JT Baker JTB-100 or JTB-111 may also be used). Cleaning removesparticles from the bonding surfaces, and makes the surface energy known,i.e., it provides a base-line of surface energy. The manner of cleaningneed not be SC1, other types of cleaning may be used, as the type ofcleaning is likely to have only a very minor effect on the silanolgroups on the surface. The results for various tests are set forth belowin Table 1.

A strong but separable initial, room temperature or van der Waal and/orHydrogen-bond was created by simply cleaning a thin glass sheet of 100mm square×100 micron thick, and a glass carrier 150 mm diameter singlemean flat (SMF) wafer 0.50 or 0.63 mm thick, each comprising Eagle XG®display glass (an alkali-free, alumino-boro-silicate glass, having anaverage surface roughness Ra on the order of 0.2 nm, available fromCorning Incorporated, Corning, N.Y.). In this example, glass was cleaned10 min in a 65° C. bath of 40:1:2 DI water: JTB-111:Hydrogen peroxide.The thin glass or glass carrier may or may not have been annealed innitrogen for 10 min at 400° C. to remove residual water—the notation“400° C.” in the “Carrier” column or the “Thin Glass” column in Table 1below indicates that the sample was annealed in nitrogen for 10 minutesat 400° C. FPD process compatibility testing demonstrates this SC1-SC1initial, room temperature, bond is mechanically strong enough to passvacuum, SRD and ultrasonic testing. However, heating at 400° C. andabove created a permanent bond between the thin glass and carrier, i.e.,the thin glass sheet could not be removed from the carrier withoutdamaging either one or both of the thin glass sheet and carrier. Andthis was the case even for Example 1c, wherein each of the carrier andthe thin glass had an annealing step to reduce the concentration ofsurface hydroxyls. Accordingly, the above-described preparation of thebonding surfaces 14, 24 via heating alone and then bonding of thecarrier 10 and the thin sheet 12, without a surface modification layer30, is not a suitable controlled bond for processes wherein thetemperature will be ≧400° C.

TABLE 1 process compatibility testing of SC1-treated glass bondingsurfaces Thin Ultra- Example Carrier Glass Vacuum SRD 400 C. 600 C.sonic 1a SC1 SC1 P P F F P 1b SC1, SC1 P P F F P 400 C. 1c SC1, SC1, P PF F P 400 C. 400 C.

Preparation of Bonding Surfaces by Hydroxyl Reduction and SurfaceModification Layer

Hydroxyl reduction, as by heat treatment for example, and a surfacemodification layer 30 may be used together to control the interaction ofbonding surfaces 14, 24. For example, the bonding energy (both van derWaals and/or Hydrogen-bonding at room temperature due to thepolar/dispersion energy components, and covalent bonding at hightemperature due to the covalent energy component) of the bondingsurfaces 14, 24 can be controlled so as to provide varying bond strengthfrom that wherein room-temperature bonding is difficult, to thatallowing easy room-temperature bonding and separation of the bondingsurfaces after high temperature processing, to that which—after hightemperature processing—prevents the surfaces from separating withoutdamage. In some applications, it may be desirable to have no, or veryweak bonding. In other applications, for example providing a carrier forhigh temperature processes (wherein process temperatures ≧500° C., or≧600° C., and up to 650° C., may be achieved), it is desirable to havesufficient van der Waals and/or Hydrogen-bonding, at room temperature toinitially put the thin sheet and carrier together, and yet prevent orlimit high temperature covalent bonding. For still other applications,it may be desirable to have sufficient room temperature bonding toinitially put the thin sheet and carrier together, and also to developstrong covalent bonding at high temperature. Although not wishing to bebound by theory, in some instances the surface modification layer may beused to control room temperature bonding by which the thin sheet andcarrier are initially put together, whereas the reduction of hydroxylgroups on the surface (as by heating the surface, or by reaction of thehydroxyl groups with the surface modification layer, for example) may beused to control the covalent bonding, particularly that at hightemperatures.

A material for the surface modification layer 30 may provide a bondingsurface 14, 24 with an energy (for example, and energy ≦40 mJ/m², asmeasured for one surface, and including polar and dispersion components)whereby the surface produces only weak bonding. In one example,hexamethyldisilazane (HMDS) may be used to create this low energysurface by reacting with the surface hydroxyls to leave a trimethylsilyl(TMS) terminated surface. HMDS as a surface modification layer may beused together with surface heating to reduce the hydroxyl concentrationto control both room temperature and high temperature bonding. Bychoosing a suitable bonding surface preparation for each bonding surface14, 24, there can be achieved articles having a range of capabilities.More specifically, of interest to high temperature processing, there canbe achieved a suitable bond between a thin sheet 20 and a carrier 10 soas to survive (or pass) each of the vacuum SRD, 400° C. (parts a and c),and 600° C. (parts a and c), processing tests.

In one example, following SC1 cleaning by HMDS treatment of both thinglass and carrier creates a weakly bonded surface which is challengingto bond at room temperature with van der Waals (and/or hydrogen bonding)forces. Mechanical force is applied to bond the thin glass to thecarrier. As shown in example 2a of Table 2, this bonding is sufficientlyweak that deflection of the carrier is observed in vacuum testing andSRD processing, bubbling (likely due to outgassing) was observed in 400°C. and 600° C. thermal processes, and particulate defects were observedafter ultrasonic processing.

In another example, HMDS treatment of just one surface (carrier in theexample cited) creates stronger room temperature adhesion which survivesvacuum and SRD processing. However, thermal processes at 400° C. andabove permanently bonded the thin glass to the carrier. This is notunexpected as the maximum surface coverage of the trimethylsilyl groupson silica has been calculated by Sindorf and Maciel in J. Phys. Chem.1982, 86, 5208-5219 to be 2.8/nm² and measured by Suratwala et. al. inJournal of Non-Crystalline Solids 316 (2003) 349-363 as 2.7/nm², vs. ahydroxyl concentration of 4.6-4.9/nm² for fully hydroxylated silica.That is, although the trimethylsilyl groups do bond with some surfacehydroxyls, there will remain some un-bonded hydroxyls. Thus one wouldexpect condensation of surface silanol groups to permanently bond thethin glass and carrier given sufficient time and temperature.

A varied surface energy can be created by heating the glass surface toreduce the surface hydroxyl concentration prior to HMDS exposure,leading to an increased polar component of the surface energy. This bothdecreases the driving force for formation of covalent Si—O—Si bonds athigh temperature and leads to stronger room-temperature bonding, forexample, van der Waal (and/or hydrogen) bonding. FIG. 4 shows thesurface energy of an Eagle XG® display glass carrier after annealing,and after HMDS treatment. Increased annealing temperature prior to HMDSexposure increases the total (polar and dispersion) surface energy (line402) after HMDS exposure by increasing the polar contribution (line404). It is also seen that the dispersion contribution (line 406) to thetotal surface energy remains largely unchanged by the heat treatment.Although not wishing to be bound by theory, increasing the polarcomponent of, and thereby the total, energy in the surface after HMDStreatment appears to be due to there being some exposed glass surfaceareas even after HMDS treatment because of sub-monolayer TMS coverage bythe HMDS.

In example 2b, the thin glass sheet was heated at a temperature of 150°C. in a vacuum for one hour prior to bonding with the non-heat-treatedcarrier having a coating of HMDS. This heat treatment of the thin glasssheet was not sufficient to prevent permanent bonding of the thin glasssheet to the carrier at temperatures ≧400° C.

As shown in examples 2c-2e of Table 2, varying the annealing temperatureof the glass surface prior to HMDS exposure can vary the bonding energyof the glass surface so as to control bonding between the glass carrierand the thin glass sheet.

In example 2c, the carrier was annealed at a temperature of 190° C. invacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Additionally, the thin glass sheet was annealedat 450° C. in a vacuum for 1 hour before bonding with the carrier. Theresulting article survived the vacuum, SRD, and 400° C. tests (parts aand c, but did not pass part b as there was increased bubbling), butfailed the 600° C. test. Accordingly, although there was increasedresistance to high temperature bonding as compared with example 2b, thiswas not sufficient to produce an article for processing at temperatures≧600° C. wherein all of the thin sheet may be removed from the carrier.

In example 2d, the carrier was annealed at a temperature of 340° C. in avacuum for 1 hour, followed by HMDS exposure to provide surfacemodification layer 30. Again, the thin glass sheet was annealed at 450°C. for 1 hour in a vacuum before bonding with the carrier. The resultswere similar to those for example 2c, wherein the article survived thevacuum, SRD, and 400° C. tests (parts a and c, but did not pass part bas there was increased bubbling), but failed the 600° C. test.

As shown in example 2e, annealing both thin glass and carrier at 450° C.in vacuum for 1 hour, followed by HMDS exposure of the carrier, and thenbonding of the carrier and thin glass sheet, improves the temperatureresistance to permanent bonding. An anneal of both surfaces to 450° C.prevents permanent bonding after RTP annealing at 600° C. for 10 min,that is, this sample passed the 600° C. processing test (parts a and c,but did not pass part b as there was increased bubbling; a similarresult was found for the 400° C. test).

TABLE 2 process compatibility testing of HMDS surface modificationlayers Example Carrier Thin Glass Vacuum SRD 400 C. 600 C. Ultrasonic 2aSC1, HMDS SC1, HMDS F F P P F 2b SC1, HMDS SC1, 150 C. P P F F 2c SC1,190 C., HMDS SC1, 450 C. P P P F 2d SC1, 340 C., HMDS SC1, 450 C. P P PF 2e SC1, 450 C., HMDS SC1, 450 C. P P P P

In Examples 2a to 2e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.The HMDS was applied by pulse vapor deposition in a YES-5 HMDS oven(available from Yield Engineering Systems, San Jose Calif.) and was oneatomic layer thick (i.e., about 0.2 to 1 nm), although the surfacecoverage may be less than one monolayer, i.e., some of the surfacehydroxyls are not covered by the HMDS as noted by Maciel and discussedabove. Because of the small thickness in the surface modification layer,there is little risk of outgassing which can cause contamination in thedevice fabrication. Also, as indicated in Table 2 by the “SC1” notation,each of the carriers and thin sheets were cleaned using an SC1 processprior to heat treating or any subsequent HMDS treatment.

A comparison of example 2a with example 2b shows that the bonding energybetween the thin sheet and the carrier can be controlled by varying thenumber of surfaces which include a surface modification layer. Andcontrolling the bonding energy can be used to control the bonding forcebetween two bonding surfaces. Also, a comparison of examples 2b-2e,shows that the bonding energy of a surface can be controlled by varyingthe parameters of a heat treatment to which the bonding surface issubjected before application of a surface modification material. Again,the heat treatment can be used to reduce the number of surface hydroxylsand, thus, control the degree of covalent bonding, especially that athigh temperatures.

Other materials, that may act in a different manner to control thesurface energy on a bonding surface, may be used for the surfacemodification layer 30 so as to control the room temperature and hightemperature bonding forces between two surfaces. For example, a thinsheet that may be completely removed from a carrier can also be createdif one or both bonding surfaces are modified to create a moderatebonding force with a surface modification layer that either covers, orsterically hinders species for example hydroxyls to prevent theformation at elevated temperature of strong permanent covalent bondsbetween carrier and thin sheet. One way to create a tunable surfaceenergy, and cover surface hydroxyls to prevent formation of covalentbonds, is deposition of plasma polymer films, for example fluoropolymerfilms. Plasma polymerization deposits a thin polymer film underatmospheric or reduced pressure and plasma excitation (DC or RF parallelplate, Inductively Coupled Plasma (ICP) Electron Cyclotron Resonance(ECR) downstream microwave or RF plasma) from source gases for examplefluorocarbon sources (including CF4, CHF3, C2F6, C3F6, C2F2, CH3F, C4F8,chlorofluoro carbons, or hydrochlorofluoro carbons), hydrocarbons forexample alkanes (including methane, ethane, propane, butane), alkenes(including ethylene, propylene), alkynes (including acetylene), andaromatics (including benzene, toluene), hydrogen, and other gas sourcesfor example SF6. Plasma polymerization creates a layer of highlycross-linked material. Control of reaction conditions and source gasescan be used to control the film thickness, density, and chemistry totailor the functional groups to the desired application.

FIG. 5 shows the total (line 502) surface energy (including polar (line504) and dispersion (line 506) components) of plasma polymerizedfluoropolymer (PPFP) films deposited from CF4-C4F8 mixtures with anOxford ICP380 etch tool (available from Oxford Instruments, OxfordshireUK). The films were deposited onto a sheet of Eagle XG® glass, andspectroscopic ellipsometry showed the films to be 1-10 nm thick. As seenfrom FIG. 5, glass carriers treated with plasma polymerizedfluoropolymer films containing less than 40% C4F8 exhibit a surfaceenergy ≧40 mJ/m² and produce controlled bonding between the thin glassand carrier at room temperature by van der Waal or hydrogen bonding.Facilitated bonding is observed when initially bonding the carrier andthin glass at room temperature. That is, when placing the thin sheetonto the carrier, and pressing them together at a point, a wave fronttravels across the carrier, but at a lower speed than is observed forSC1 treated surfaces having no surface modification layer thereon. Thecontrolled bonding is sufficient to withstand all standard FPD processesincluding vacuum, wet, ultrasonic, and thermal processes up to 600° C.,that is this controlled bonding passed the 600° C. processing testwithout movement or delamination of the thin glass from the carrier.De-bonding was accomplished by peeling with a razor blade and/or Kapton™tape as described above. The process compatibility of two different PPFPfilms (deposited as described above) is shown in Table 3. PPFP 1 ofexample 3a was formed with C4F8/(C4F8+CF4)=0, that is, formed withCF4/H2 and not C4F8, and PPFP 2 of example 3b was deposited withC4F8/(C4F8+CF4)=0.38. Both types of PPFP films survived the vacuum, SRD,400° C. and 600° C. processing tests. However, delamination is observedafter 20 min of ultrasonic cleaning of PPFP 2 indicating insufficientadhesive force to withstand such processing. Nonetheless, the surfacemodification layer of PPFP2 may be useful for some applications, aswhere ultrasonic processing is not necessary.

TABLE 3 process compatibility testing of PPFP surface modificationlayers Thin Ultra- Example Carrier Glass Vacuum SRD 400 C. 600 C. sonic3a PPFP 1 SC1, P P P P P 150 C. 3b PPFP2 SC1, P P P P F 150 C.

In Examples 3a and 3b above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.Because of the small thickness in the surface modification layer, thereis little risk of outgassing which can cause contamination in the devicefabrication. Further, because the surface modification layer did notappear to degrade, again, there is even less risk of outgassing. Also,as indicated in Table 3, each of the thin sheets was cleaned using anSC1 process prior to heat treating at 150° C. for one hour in a vacuum.

Still other materials, that may function in a different manner tocontrol surface energy, may be used as the surface modification layer tocontrol the room temperature and high temperature bonding forces betweenthe thin sheet and the carrier. For example, a bonding surface that canproduce controlled bonding can be created by silane treating a carrierand/or glass thin sheet. Silanes are chosen so as to produce a suitablesurface energy, and so as to have sufficient thermal stability for theapplication. The carrier or thin sheet to be treated may be cleaned by aprocess for example O2 plasma or UV-ozone, and SC1 or standard clean two(SC2, as is known in the art) cleaning to remove organics and otherimpurities (metals, for example) that would interfere with the silanereacting with the surface silanol groups. Washes based on otherchemistries may also be used, for example, HF, or H2SO4 washchemistries. The carrier or thin sheet may be heated to control thesurface hydroxyl concentration prior to silane application (as discussedabove in connection with the surface modification layer of HMDS), and/ormay be heated after silane application to complete silane condensationwith the surface hydroxyls. The concentration of unreacted hydroxylgroups after silanization may be made low enough prior to bonding as toprevent permanent bonding between the thin sheet and carrier attemperatures ≧400° C., that is, to form a controlled bond. This approachis described below.

Example 4a

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% dodecyltriethoxysilane (DDTS) in toluene, andannealed at 150° C. in vacuum for 1 hour to complete condensation. DDTStreated surfaces exhibit a surface energy of 45 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and heated at 400° C. ina vacuum for one hour) was bonded to the carrier bonding surface havingthe DDTS surface modification layer thereon. This article survived wetand vacuum process tests but did not survive thermal processes over 400°C. without bubbles forming under the carrier due to thermaldecomposition of the silane. This thermal decomposition is expected forall linear alkoxy and chloro alkylsilanes R1_(x)Si(OR2)_(y)(Cl)_(z)where x=1 to 3, and y+z=4-x except for methyl, dimethyl, and trimethylsilane (x=1 to 3, R1=CH₃) which produce coatings of good thermalstability.

Example 4b

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 3,3,3, trifluoropropyltritheoxysilane (TFTS) intoluene, and annealed at 150° C. in vacuum for 1 hour to completecondensation. TFTS treated surfaces exhibit a surface energy of 47mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the TFTS surface modification layerthereon. This article survived the vacuum, SRD, and 400° C. processtests without permanent bonding of the glass thin sheet to the glasscarrier. However, the 600° C. test produced bubbles forming under thecarrier due to thermal decomposition of the silane. This was notunexpected because of the limited thermal stability of the propyl group.Although this sample failed the 600° C. test due to the bubbling, thematerial and heat treatment of this example may be used for someapplications wherein bubbles and the adverse effects thereof, forexample reduction in surface flatness, or increased waviness, can betolerated.

Example 4c

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% phenyltriethoxysilane (PTS) in toluene, andannealed at 200° C. in vacuum for 1 hour to complete condensation. PTStreated surfaces exhibit a surface energy of 54 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the PTS surface modification layer. This article survived thevacuum, SRD, and thermal processes up to 600° C. without permanentbonding of the glass thin sheet with the glass carrier.

Example 4d

A glass carrier with its bonding surface O2 plasma and SC1 treated wasthen treated with 1% diphenyldiethoxysilane (DPDS) in toluene, andannealed at 200° C. in vacuum for 1 hour to complete condensation. DPDStreated surfaces exhibit a surface energy of 47 mJ/m². As shown in Table4, a glass thin sheet (having been SC1 cleaned and then heated at 400°C. in a vacuum for one hour) was bonded to the carrier bonding surfacehaving the DPDS surface modification layer. This article survived thevacuum and SRD tests, as well as thermal processes up to 600° C. withoutpermanent bonding of the glass thin sheet with the glass carrier.

Example 4e

A glass carrier having its bonding surface O2 plasma and SC1 treated wasthen treated with 1% 4-pentafluorophenyltriethoxysilane (PFPTS) intoluene, and annealed at 200° C. in vacuum for 1 hour to completecondensation. PFPTS treated surfaces exhibit a surface energy of 57mJ/m². As shown in Table 4, a glass thin sheet (having been SC1 cleanedand then heated at 400° C. in a vacuum for one hour) was bonded to thecarrier bonding surface having the PFPTS surface modification layer.This article survived the vacuum and SRD tests, as well as thermalprocesses up to 600° C. without permanent bonding of the glass thinsheet with the glass carrier.

TABLE 4 process compatibility testing of silane surface modificationlayers Example Carrier Thin Glass Vacuum SRD 400 C. 600 C. 4a SC1, DDTSSC1, 400 C. P P F F 4b SC1, TFTS SC1, 400 C. P P P F 4c SC1, PTS SC1,400 C. P P P P 4d SC1, DPDS SC1, 400 C. P P P P 4e SC1, PFPTS SC1, 400C. P P P P

In Examples 4a to 4e above, each of the carrier and the thin sheet wereEagle XG® glass, wherein the carrier was a 150 mm diameter SMF wafer 630microns thick and the thin sheet was 100 mm square 100 microns thick.The silane layers were self-assembled monolayers (SAM), and thus were onthe order of less than about 2 nm thick. In the above examples, the SAMwas created using an organosilane with an aryl or alkyl non-polar tailand a mono, di, or tri-alkoxide head group. These react with the silanolsurface on the glass to directly attach the organic functionality.Weaker interactions between the non-polar head groups organize theorganic layer. Because of the small thickness in the surfacemodification layer, there is little risk of outgassing which can causecontamination in the device fabrication. Further, because the surfacemodification layer did not appear to degrade in examples 4c, 4d, and 4e,again, there is even less risk of outgassing. Also, as indicated inTable 4, each of the glass thin sheets was cleaned using an SC1 processprior to heat treating at 400° C. for one hour in a vacuum.

As can be seen from a comparison of examples 4a-4e, controlling surfaceenergy of the bonding surfaces to be above 40 mJ/m² so as to facilitatethe initial room temperature bonding is not the only consideration tocreating a controlled bond that will withstand FPD processing and stillallow the thin sheet to be removed from the carrier without damage.Specifically, as seen from examples 4a-4e, each carrier had a surfaceenergy above 40 mJ/m², which facilitated initial room temperaturebonding so that the article survived vacuum and SRD processing. However,examples 4a and 4b did not pass 600° C. processing test. As noted above,for certain applications, it is also important for the bond to surviveprocessing up to high temperatures (for example, ≧400° C., ≧500° C., or≧600° C., up to 650° C., as appropriate to the processes in which thearticle is designed to be used) without degradation of the bond to thepoint where it is insufficient to hold the thin sheet and carriertogether, and also to control the covalent bonding that occurs at suchhigh temperatures so that there is no permanent bonding between the thinsheet and the carrier. As shown by the examples in Table 4, aromaticsilanes, in particular phenyl silanes, are useful for providing acontrolled bond that will facilitate initial room temperature bonding,and that will withstand high temperature processing and still allow thethin sheet to be removed from the carrier without damage.

The above-described separation in examples 4, 3, and 2, is performed atroom temperature without the addition of any further thermal or chemicalenergy to modify the bonding interface between the thin sheet andcarrier. The only energy input is mechanical pulling and/or peelingforce.

The materials described above in examples 3 and 4 can be applied to thecarrier, to the thin sheet, or to both the carrier and thin sheetsurfaces that will be bonded together.

Outgassing

Polymer adhesives used in typical wafer bonding applications aregenerally 10-100 microns thick and lose about 5% of their mass at ornear their temperature limit. For such materials, evolved from thickpolymer films, it is easy to quantify the amount of mass loss, oroutgassing, by mass-spectrometry. On the other hand, it is morechallenging to measure the outgassing from thin surface treatments thatare on the order of 10 nm thick or less, for example the plasma polymeror self-assembled monolayer surface modification layers described above,as well as for a thin layer of pyrolyzed silicone oil. For suchmaterials, mass-spectrometry is not sensitive enough. There are a numberof other ways to measure outgassing, however.

A first manner of measuring small amounts of outgassing is based onsurface energy measurements, and will be described with reference toFIG. 6. To carry out this test, a setup as shown in FIG. 6 may be used.A first substrate, or carrier, 900 having the to-be-tested surfacemodification layer thereon presents a surface 902, i.e., a surfacemodification layer corresponding in composition and thickness to thesurface modification layer 30 to be tested. A second substrate, orcover, 910 is placed so that its surface 912 is in close proximity tothe surface 902 of the carrier 900, but not in contact therewith. Thesurface 912 is an uncoated surface, i.e., a surface of bare materialfrom which the cover is made. Spacers 920 are placed at various pointsbetween the carrier 900 and cover 910 to hold them in spaced relationfrom one another. The spacers 920 should be thick enough to separate thecover 910 from the carrier 900 to allow a movement of material from oneto the other, but thin enough so that during testing the amount ofcontamination from the chamber atmosphere on the surfaces 902 and 912 isminimized. The carrier 900, spacers 920, and cover 910, together form atest article 901.

Prior to assembly of the test article 901, the surface energy of baresurface 912 is measured, as is the surface energy of the surface 902,i.e., the surface of carrier 900 having the surface modification layerprovided thereon. The surface energies as shown in FIG. 7, both polarand dispersion components, were measured by fitting a theoretical modeldeveloped by S. Wu (1971) to three contact angles of three test liquids;water, diiodomethane and hexadecane. (Reference: S. Wu, J. Polym. Sci.C, 34, 19, 1971).

After assembly, the test article 901 is placed into a heating chamber930, and is heated through a time-temperature cycle. The heating isperformed at atmospheric pressure and under flowing N2 gas, i.e.,flowing in the direction of arrows 940 at a rate of 2 standard litersper minute.

During the heating cycle, changes in the surface 902 (including changesto the surface modification layer due to evaporation, pyrolysis,decomposition, polymerization, reaction with the carrier, andde-wetting, for example) are evidenced by a change in the surface energyof surface 902. A change in the surface energy of surface 902 by itselfdoes not necessarily mean that the surface modification layer hasoutgassed, but does indicate a general instability of the material atthat temperature as its character is changing due to the mechanismsnoted above, for example. Thus, the less the change in surface energy ofsurface 902, the more stable the surface modification layer. On theother hand, because of the close proximity of the surface 912 to thesurface 902, any material outgassed from surface 902 will be collectedon surface 912 and will change the surface energy of surface 912.Accordingly, the change in surface energy of surface 912 is a proxy foroutgassing of the surface modification layer present on surface 902.

Thus, one test for outgassing uses the change in surface energy of thecover surface 912. Specifically, if there is a change in surfaceenergy—of surface 912—of ≧10 mJ/m2, then there is outgassing. Changes insurface energy of this magnitude are consistent with contamination whichcan lead to loss of film adhesion or degradation in material propertiesand device performance. A change in surface energy of ≦5 mJ/m2 is closeto the repeatability of surface energy measurements and inhomogeneity ofthe surface energy. This small change is consistent with minimaloutgassing.

During testing that produced the results in FIG. 7, the carrier 900, thecover 910, and the spacers 920, were made of Eagle XG glass, analkali-free alumino-boro-silicate display-grade glass available fromCorning Incorporated, Corning, N.Y., although such need not be the case.The carrier 900 and cover 910 were 150 mm diameter 0.63 mm thick.Generally, the carrier 910 and cover 920 will be made of the samematerial as carrier 10 and thin sheet 20, respectively, for which anoutgassing test is desired. During this testing, silicon spacers 0.63 mmthick, 2 mm wide, and 8 cm long, thereby forming a gap of 0.63 mmbetween surfaces 902 and 912. During this testing, the chamber 930 wasincorporated in MPT-RTP600s rapid thermal processing equipment that wascycled from room temperature to the test limit temperature at a rate of9.2° C. per minute, held at the test limit temperature for varying timesas shown in the graphs as “Anneal Time”, and then cooled at furnace rateto 200° C. After the oven had cooled to 200° C., the test article wasremoved, and after the test article had cooled to room temperature, thesurface energies of each surface 902 and 912 were again measured. Thus,by way of example, using the data for the change in cover surfaceenergy, tested to a limit temperature of 450° C., for Material #1, line1003, the data was collected as follows. The data point at 0 minutesshows a surface energy of 75 mJ/m2 (milli-Joules per square meter), andis the surface energy of the bare glass, i.e., there has been notime-temperature cycle yet run. The data point at one minute indicatesthe surface energy as measured after a time-temperature cycle performedas follows: the article 901 (having Material #1 used as a surfacemodification layer on the carrier 900 to present surface 902) was placedin a heating chamber 930 at room temperature, and atmospheric pressure;the chamber was heated to the test-limit temperature of 450° C. at arate of 9.2° C. per minute, with a N2 gas flow at two standard litersper minute, and held at the test-limit temperature of 450° C. for 1minute; the chamber was then allowed to cool to 300° C. at a rate of 1°C. per minute, and the article 901 was then removed from the chamber930; the article was then allowed to cool to room temperature (withoutN2 flowing atmosphere); the surface energy of surface 912 was thenmeasured and plotted as the point for 1 minute on line 1003. Theremaining data points for Material #1 (lines 1003, 1004), as well as thedata points for Material #2 (lines 1203, 1204), Material #3 (lines 1303,1304), Material #4 (lines 1403, 1404), Material #5 (lines 1503, 1504),and Material #6 (lines 1603, and 1604), were then determined in asimilar manner with the minutes of anneal time corresponding to the holdtime at the test-limit temperature, either 450° C., or 600° C., asappropriate. The data points for lines 1001, 1002, 1201, 1202, 1301,1302, 1401, 1402, 1501, 1502, 1601, and 1602, representing surfaceenergy of surface 902 for the corresponding surface modification layermaterials (Materials #1-6) were determined in a similar manner, exceptthat the surface energy of the surface 902 was measured after eachtime-temperature cycle.

The above assembly process, and time-temperature cycling, were carriedout for six different materials as set forth below, and the results aregraphed in FIG. 7. Of the six materials, Materials #1-4 correspond tosurface modification layer materials described above. Materials #5 and#6 are comparative examples.

Material #1 is a CHF3-CF4 plasma polymerized fluoropolymer. Thismaterial is consistent with the surface modification layer in example3b, above. As shown in FIG. 7, lines 1001 and 1002 show that the surfaceenergy of the carrier did not significantly change. Thus, this materialis very stable at temperatures from 450° C. to 600° C. Additionally, asshown by the lines 1003 and 1004, the surface energy of the cover didnot significantly change either, i.e., the change is ≦5 mJ/m2.Accordingly, there was no outgassing associated with this material from450° C. to 600° C.

Material #2 is a phenylsilane, a self-assembled monolayer (SAM)deposited form 1% toluene solution of phenyltriethoxysilane and cured invacuum oven 30 minutes at 190° C. This material is consistent with thesurface modification layer in example 4c, above. As shown in FIG. 7,lines 1201 and 1202 indicate some change in surface energy on thecarrier. As noted above, this indicates some change in the surfacemodification layer, and comparatively, Material #2 is somewhat lessstable than Material #1. However, as noted by lines 1203 and 1204, thechange in surface energy of the carrier is ≦5 mJ/m2, showing that thechanges to the surface modification layer did not result in outgassing.

Material #3 is a pentafluorophenylsilane, a SAM deposited from 1%toluene solution of pentafluorophenyltriethoxysilane and cured in vacuumoven 30 minutes at 190° C. This material is consistent with the surfacemodification layer in example 4e, above. As shown in FIG. 7, lines 1301and 1302 indicate some change in surface energy on the carrier. As notedabove, this indicates some change in the surface modification layer, andcomparatively, Material #3 is somewhat less stable than Material #1.However, as noted by lines 1303 and 1304, the change in surface energyof the carrier is ≦5 mJ/m2, showing that the changes to the surfacemodification layer did not result in outgassing.

Material #4 is hexamethyldisilazane (HMDS) deposited from vapor in a YESHMDS oven at 140° C. This material is consistent with the surfacemodification layer in Example 2b, of Table 2, above. As shown in FIG. 7,lines 1401 and 1402 indicate some change in surface energy on thecarrier. As noted above, this indicates some change in the surfacemodification layer, and comparatively, Material #4 is somewhat lessstable than Material #1. Additionally, the change in surface energy ofthe carrier for Material #4 is greater than that for any of Materials #2and #3 indicating, comparatively, that Material #4 is somewhat lessstable than Materials #2 and #3. However, as noted by lines 1403 and1404, the change in surface energy of the carrier is ≦5 mJ/m2, showingthat the changes to the surface modification layer did not result inoutgassing that affected the surface energy of the cover. However, thisis consistent with the manner in which HMDS outgasses. That is, HMDSoutgasses ammonia and water which do not affect the surface energy ofthe cover, and which may not affect some electronics fabricationequipment and/or processing. On the other hand, when the products of theoutgassing are trapped between the thin sheet and carrier, there may beother problems, as noted below in connection with the second outgassingtest.

Material #5 is Glycidoxypropylsilane, a SAM deposited from 1% toluenesolution of glycidoxypropyltriethoxysilane and cured in vacuum oven 30minutes at 190° C. This is a comparative example material. Althoughthere is relatively little change in the surface energy of the carrier,as shown by lines 1501 and 1502, there is significant change in surfaceenergy of the cover as shown by lines 1503 and 1504. That is, althoughMaterial #5 was relatively stable on the carrier surface, it did, indeedoutgas a significant amount of material onto the cover surface wherebythe cover surface energy changed by ≧10 mJ/m2. Although the surfaceenergy at the end of 10 minutes at 600° C. is within 10 mJ/m2, thechange during that time does exceed 10 mJ/m2. See, for example the datapoints at 1 and 5 minutes. Although not wishing to be bound by theory,the slight uptick in surface energy from 5 minutes to 10 minutes islikely do to some of the outgassed material decomposing and falling offof the cover surface.

Material #6 is DC704 a silicone coating prepared by dispensing 5 ml DowCorning 704 diffusion pump oil tetramethyltetraphenyl trisiloxane(available from Dow Corning) onto the carrier, placing it on a 500° C.hot plate in air for 8 minutes. Completion of sample preparation isnoted by the end of visible smoking. After preparing the sample in theabove manner, the outgassing testing described above was carried out.This is a comparative example material. As shown in FIG. 7, lines 1601and 1602 indicate some change in surface energy on the carrier. As notedabove, this indicates some change in the surface modification layer, andcomparatively, Material #6 is less stable than Material #1.Additionally, as noted by lines 1603 and 1604, the change in surfaceenergy of the carrier is ≧10 mJ/m2, showing significant outgassing. Moreparticularly, at the test-limit temperature of 450° C., the data pointfor 10 minutes shows a decrease in surface energy of about 15 mJ/m2, andeven greater decrease in surface energy for the points at 1 and 5minutes. Similarly, the change in surface energy of the cover duringcycling at the 600° C. test-limit temperature, the decrease in surfaceenergy of the cover was about 25 mJ/m2 at the 10 minute data point,somewhat more at 5 minutes, and somewhat less at 1 minute. Altogether,though, a significant amount of outgassing was shown for this materialover the entire range of testing.

Significantly, for Materials #1-4, the surface energies throughout thetime-temperature cycling indicate that the cover surface remains at asurface energy consistent with that of bare glass, i.e., there iscollected no material outgassed from the carrier surface. In the case ofMaterial #4, as noted in connection with Table 2, the manner in whichthe carrier and thin sheet surfaces are prepared makes a big differencein whether an article (thin sheet bonded together with a carrier via asurface modification layer) will survive FPD processing. Thus, althoughthe example of Material #4 shown in FIG. 7 may not outgas, this materialmay or may not survive the 400° C. or 600° C. tests as noted inconnection with the discussion of Table 2.

A second manner of measuring small amounts of outgassing is based on anassembled article, i.e., one in which a thin sheet is bonded to acarrier via a surface modification layer, and uses a change in percentbubble area to determine outgassing. That is, during heating of thearticle, bubbles formed between the carrier and the thin sheet indicateoutgassing of the surface modification layer. As noted above inconnection with the first outgassing test, it is difficult to measureoutgassing of very thin surface modification layers. In this secondtest, the outgassing under the thin sheet may be limited by strongadhesion between the thin sheet and carrier. Nonetheless, layers ≦10 nmthick (plasma polymerized materials, SAMs, and pyrolyzed silicone oilsurface treatments, for example) may still create bubbles during thermaltreatment, despite their smaller absolute mass loss. And the creation ofbubbles between the thin sheet and carrier may cause problems withpattern generation, photolithography processing, and/or alignment duringdevice processing onto the thin sheet. Additionally, bubbling at theboundary of the bonded area between the thin sheet and the carrier maycause problems with process fluids from one process contaminating adownstream process. A change in % bubble area of ≧5 is significant,indicative of outgassing, and is not desirable. On the other hand achange in % bubble area of ≦1 is insignificant and an indication thatthere has been no outgassing.

The average bubble area of bonded thin glass in a class 1000 clean roomwith manual bonding is 1%. The % bubbles in bonded carriers is afunction of cleanliness of the carrier, thin sheet, and surfacepreparation. Because these initial defects act as nucleation sites forbubble growth after heat treatment, any change in bubble area upon heattreatment less than 1% is within the variability of sample preparation.To carry out this test, a commercially available desktop scanner withtransparency unit (Epson Expression 10000XL Photo) was used to make afirst scan image of the area bonding the thin sheet and carrierimmediately after bonding. The parts were scanned using the standardEpson software using 508 dpi (50 micron/pixel) and 24 bit RGB. The imageprocessing software first prepares an image by stitching, as necessary,images of different sections of a sample into a single image andremoving scanner artifacts (by using a calibration reference scanperformed without a sample in the scanner). The bonded area is thenanalyzed using standard image processing techniques such asthresholding, hole filling, erosion/dilation, and blob analysis. Thenewer Epson Expression 11000XL Photo may also be used in a similarmanner. In transmission mode, bubbles in the bonding area are visible inthe scanned image and a value for bubble area can be determined. Then,the bubble area is compared to the total bonding area (i.e., the totaloverlap area between the thin sheet and the carrier) to calculate a %area of the bubbles in the bonding area relative to the total bondingarea. The samples are then heat treated in a MPT-RTP600s Rapid ThermalProcessing system under N2 atmosphere at test-limit temperatures of 300°C., 450° C., and 600° C., for up to 10 minutes. Specifically, thetime-temperature cycle carried out included: inserting the article intothe heating chamber at room temperature and atmospheric pressure; thechamber was then heated to the test-limit temperature at a rate of 9° C.per minute; the chamber was held at the test-limit temperature for 10minutes; the chamber was then cooled at furnace rate to 200° C.; thearticle was removed from the chamber and allowed to cool to roomtemperature; the article was then scanned a second time with the opticalscanner. The % bubble area from the second scan was then calculated asabove and compared with the % bubble area from the first scan todetermine a change in % bubble area (Δ% bubble area). As noted above, achange in bubble area of ≧5% is significant and an indication ofoutgassing. A change in % bubble area was selected as the measurementcriterion because of the variability in original % bubble area. That is,most surface modification layers have a bubble area of about 2% in thefirst scan due to handling and cleanliness after the thin sheet andcarrier have been prepared and before they are bonded. However,variations may occur between materials. The same Materials #1-6 setforth with respect to the first outgassing test method were again usedin this second outgassing test method. Of these materials, Materials#1-4 exhibited about 2% bubble area in the first scan, whereas Materials#5 and #6 showed significantly larger bubble area, i.e., about 4%, inthe first scan.

The results of the second outgassing test will be described withreference to FIGS. 8 and 9. The outgassing test results for Materials#1-3 are shown in FIG. 8, whereas the outgassing test results forMaterials #4-6 are shown in FIG. 9.

The results for Material #1 are shown as square data points in FIG. 8.As can be seen from the figure, the change in % bubble area was nearzero for test-limit temperatures of 300° C., 450° C., and 600° C.Accordingly, Material #1 shows no outgassing at these temperatures.

The results for Material #2 are shown as diamond data points in FIG. 8.As can be seen from the figure, the change in % bubble area is less than1 for test-limit temperatures of 450° C. and 600° C. Accordingly,Material #2 shows no outgassing at these temperatures.

The results for Material #3 are shown as triangle data points in FIG. 8.As can be seen from the figure, similar to the results for Material #1,the change in % bubble area was near zero for test-limit temperatures of300° C., 450° C., and 600° C. Accordingly, Material #1 shows nooutgassing at these temperatures.

The results for Material #4 are shown as circle data points in FIG. 9.As can be seen from the figure, the change in % bubble area is near zerofor the test-limit temperature of 300° C., but is near 1% for somesamples at the test-limit temperatures of 450° C. and 600° C., and forother samples of that same material is about 5% at the test limittemperatures of 450° C. and 600° C. The results for Material #4 are veryinconsistent, and are dependent upon the manner in which the thin sheetand carrier surfaces are prepared for bonding with the HMDS material.The manner in which the samples perform being dependent upon the mannerin which the samples are prepared is consistent with the examples, andassociated discussion, of this material set forth in connection withTable 2 above. It was noted that, for this material, the samples havinga change in % bubble area near 1%, for the 450° C. and 600° C.test-limit temperatures, did not allow separation of the thin sheet fromthe carrier according to the separation tests set forth above. That is,a strong adhesion between the thin sheet and carrier may have limitedbubble generation. On the other hand, the samples having a change in %bubble area near 5% did allow separation of the thin sheet from thecarrier. Thus, the samples that had no outgassing had the undesiredresult of increased adhesion after temperature treatment which stickingthe carrier and thin sheet together (preventing removal of the thinsheet from the carrier), whereas the samples that allowed removal of thethin sheet and carrier had the undesired result of outgassing.

The results for Material #5 are shown in FIG. 9 as triangular datapoints. As can be seen from the figure, the change in % bubble area isabout 15% for the test-limit temperature of 300° C., and is well overthat for the higher test-limit temperatures of 450° C. and 600° C.Accordingly, Material #5 shows significant outgassing at thesetemperatures.

The results for Material #6 are shown as square data points in FIG. 9.As can be seen from this figure, the change in % bubble area is over2.5% for the test-limit temperature of 300° C., and is over 5% for thetest limit-temperatures of 450° C. and 600° C. Accordingly, Material #6shows significant outgassing at the test-limit temperatures of 450° C.and 600° C.

For Making Electronic Devices

One use of the controlled bonding as described herein is to makearticles—including those having a carrier and a thin sheet bondedthereto—which are, in turn, used to make electronic devices, forexample, TFTs, OLEDs (including an organic light emitting material), PVdevices, touch sensors, interposers, integrated circuits,resistor-capacitor circuits, and displays.

In any event, electronic device processing equipment as is currentlydesigned for thicker sheets may be used to process the glass article soas to dispose an electronic-device component, or part of the electronicdevice, onto the sheet of the article. The electronic device componentshould be disposed on the portion(s) of the thin sheet that are bondedto the carrier via the controlled bonding described above, whereby thethin sheet remains separable from the carrier even after processing tothe temperatures necessary to make the electronic device. The deviceprocessing may include processing at temperatures of ≧400° C., ≧500° C.,≧600° C., or up to 650° C., and in some instances, up to 700° C., forexample. As described above, suitable surface modification layers may bechosen so that the thin sheet remains removable from the carrier—evenafter processing to such temperatures—without damage to at least thethin sheet, and preferably without damage to both the thin sheet and thecarrier. Any number of electronic-device components may be disposed inany number of steps for doing so, until the electronic device iscomplete or at a suitable intermediate stage. The article may beassembled before the electronic device processing, or may be assembledas a part of the electronic device making process.

The device processing may include keeping the article intact throughoutthe entire device processing, or may include dicing the article at oneor more points in the process. For example, the device processing mayinclude forming one electronic-device component on the article, and thendicing the article into two or more portions that are then subject tofurther processing, i.e., disposing an additional component of theelectronic device onto the sheet or onto the electronic-device componentexisting on the sheet from disposition in a prior step. The dicing stepmay be done so that each portion of the article includes a portion ofthe thin sheet that remains bonded to the carrier, or so that only asubset of the diced portions include such an arrangement. Within any ofthe diced portions, the entire area of the thin sheet in that portionmay remain bonded to the entire area of the carrier in that portion.

After the device processing, either to completion or to an intermediatestage, the device and the portion of the thin sheet on which it isdisposed, may be removed from the carrier. The thin sheet may be removedin its entirety, or a portion thereof may be separated from a remainingportion and that portion removed from the carrier. The removal may takeplace from the article in its entirety, or from one or more of theportions diced therefrom.

Use to Process Thin Wafers in Semiconductor and/or Interposer Processing

Another use of controlled bonding via surface modification layers(including materials and the associated bonding surface heat treatment)is to provide for use of a thin sheet on a carrier to process the thinsheet in processes requiring a temperature ≧400° C. (for example ≧450°C., ≧500° C., ≧550° C., ≧600° C.), as in FEOL processing, for example.That is, the thin sheet may be a wafer that is processed at thicknesswithout having to thin it later on. Surface modification layers(including the materials and bonding surface heat treatments), asexemplified by the examples 2e, 3a, 3b, 4c, 4d, and 4e, above, may beused to provide reuse of the carrier under such temperature conditions.Specifically, these surface modification layers may be used to modifythe surface energy of the area of overlap between the bonding areas ofthe thin sheet and carrier, whereby the entire thin sheet may beseparated from the carrier after processing. The thin sheet may beseparated all at once, or may be separated in sections as, for example,when first removing devices produced on portions of the thin sheet andthereafter removing any remaining portions to clean the carrier forreuse, for example. In the event that the entire thin sheet is removedfrom the carrier, as by removal of the thin sheet as a whole, or as byremoving diced sections of the thin sheet the sum of which add to theentire thin sheet, the carrier can be reused as is by simply by placinganother thin sheet thereon. Alternatively, the carrier may be cleanedand once again prepared to carry a thin sheet by forming a surfacemodification layer anew. Because the surface modification layers preventpermanent bonding of the thin sheet with the carrier, they may be usedfor processes wherein temperatures are ≧600° C. Of course, althoughthese surface modification layers may control bonding surface energyduring processing at temperatures ≧600° C., they may also be used toproduce a thin sheet and carrier combination that will withstandprocessing at lower temperatures, for example temperatures ≧400° C. (forexample ≧450° C., ≧500° C., ≧550° C.), and may be used in such lowertemperature applications to control bonding, without outgassing (in thecase of materials of examples 3a, 3b, 4c, 4d, and 4e), for example inBEOL processing. Moreover, where the thermal processing of the articlewill not exceed 400° C., surface modification layers as exemplified bythe examples 2c, 2d, 4b may also be used in this same manner. The thinsheet may be a polysilicon or single crystal silicon wafer, siliconwafer, glass, ceramic, glass-ceramic, quartz, sapphire, having athickness of ≦200 microns, and may be processed at, for exampletemperatures ≧500° C. to form RC circuits, ICs, or other electronicdevices thereon in FEOL processing. After FEOL processing, the wafer mayeasily be removed from the carrier without damaging the electronicdevices. Before removal, however, the wafer may undergo further, lowertemperature processing, as in BEOL processing, for example.

A second use of controlled bonding via surface modification layers(including materials and the associated bonding surface heat treatments)is to fabricate an interposer. More specifically, with the use of thesurface modification layers an area of controlled bonding can be formedwherein a sufficient separation force can separate the thin sheet (or aportion thereof) from the carrier without damage to either the thinsheet or the carrier caused by the bond, yet there is maintainedthroughout processing a sufficient bonding force to hold the thin sheetrelative to the carrier. In this case, the thin sheet is an interposer,which may be a wafer made from any suitable material including silicon,polysilicon, single crystal silicon, glass, ceramic, glass-ceramic,quartz, sapphire, for example, and which may have a thickness of ≦200microns, for example.

An example of an interposer, and the fabrication thereof, will now bedescribed with reference to FIGS. 10-12.

With reference to FIG. 10, a thin sheet 20 may be bonded to a carrier 10by a controlled bonding area 40.

In this embodiment, the carrier 10, may be a glass substrate, or anothersuitable material having a similar surface energy as glass, for example,silicon, polysilicon, single crystal silicon, ceramic, glass-ceramic,sapphire, or quartz. An advantage of using a glass substrate is thatflat sheets having minimal thickness variation can be obtained at arelatively low cost, avoiding the need for expensive carrier substrates.Additionally, with glass, a high quality can be achieved in a costeffective manner. That is, a very uniform thickness glass substrate canbe made very cheaply, and used as a carrier. However, with the surfacemodification layers of the present disclosure, the carrier need not be ahigh precision carrier having a low total thickness variation as in thecase where the wafer will be thinned to final thickness. That is, when awafer on a carrier will be thinned, the carrier must have a very tightcontrol on total thickness variation because any variation in thecarrier will be present in the thinned wafer upon thinning. With thesurface modification layers of the present disclosure, which allowforming devices on the wafer when the wafer is already at finalthickness, the total thickness variation of the carrier is much lessimportant.

In this embodiment, the thin sheet 20 is used to form interposers 56.The sheet may be silicon, including polysilicon or a single crystalsilicon wafer, quartz, sapphire, ceramic, or glass, for example. Thesheet 20 may have a thickness of ≦200 microns. The interposers 56 eachhaving a perimeter 52 and an array 50 of vias, wherein the array 50 hasa perimeter 57. Although ten interposers 56 are shown, any suitablenumber—including one—may be disposed on one thin sheet 20. Forconvenience of illustration, each interposer 56 is shown as having onlyone array 50 of vias, but such need not be the case; instead anyinterposer 56 may have more than one array 50. Further, although eachinterposer is shown as having the same number of arrays 50, such neednot be the case; any number (including zero) of the interposers may havethe same number of arrays 50. Additionally, although the arrays 50 willtypically have the same number and pattern of vias, such need not be thecase. For convenience of illustration, vias 60 are shown on only one ofthe arrays 50 of one of the interposers 56, but such need not be thecase, i.e., any one or more of the remaining interposers 56 may have oneor more arrays 50 of vias 60.

Reference will now be made to FIG. 11, which is a cross-sectional viewas taken along line 11-11 in FIG. 10. The vias 60 may include throughvias or blind vias, i.e., vias that end within the thickness of thesheet 20. Vias 60 have a diameter 62, and are spaced at a pitch 64.Although the diameters 62 are shown as being the same, such need not bethe case, i.e., there may be different diameter vias in one array 50 orin different arrays 50 on one interposer 56. The diameter 62 may be from5 microns to 150 microns, for example. Similarly, although the vias 62are spaced at the same pitch 64, such need not be the case, i.e.,different pitches may be present in one array 50, or in different arrays50 on one interposer 56 or in different interposers 56 on one thin sheet20. The pitch may be such that there are from 1 to 20 vias per squaremillimeter, for example, and will depend upon the design and applicationof the interposer. Additionally, material 61 may be present in any oneor more of the vias 60. The material 61 may be an electricallyconductive material, an electrically insulating material, or acombination thereof. For example, a conductive material may be formed onthe perimeter of the via, i.e., at its outside diameter 62, and either adifferent conductive material or an insulating material may be used tofill in the remainder of the via.

Reference will now be made to FIG. 12, which is a view similar to thatin FIG. 11, but with devices/structures disposed on the interposer 56and connected to via(s) 60. As shown in FIG. 12, a device 66 may bedisposed over, and connected with, a plurality of vias 60. Device 66 mayinclude integrated circuits; MEMS; microsensors; power semiconductors;light-emitting diodes; photonic circuits; CPU; SRAM; DRAM, eDRAM; ROM,EEPROM; flash memory; interposers; embedded passive devices; andmicrodevices fabricated on or from silicon, silicon-germanium, galliumarsenide, and gallium nitride. Although only one device 66 is shown,there may be any suitable number of devices 66 on one interposer 56,including an array of devices 56. Alternatively, a structure 68 may bedisposed over and connected with only one via 60. Structures 68 mayinclude: solder bumps; metal posts; metal pillars; interconnectionroutings; interconnect lines; insulating oxide layers; and structuresformed from a material selected from the group consisting of silicon,polysilicon, silicon dioxide, silicon (oxy)nitride, metal (for example,Cu, Al, W), low k dielectrics, polymer dielectrics, metal nitrides, andmetal silicides. Although only one structure 68 is shown, there may beany suitable number of structures 68 on one interposer 56, includingarray(s) of structures 56. Further, one or more structures 68 may bedisposed on a device 66.

In the controlled bonding area 40, the carrier 10 and thin sheet 20 arebonded to one another so that over the entire area of overlap, thecarrier 10 and thin sheet 20 are connected, but may be separated fromone another, even after high temperature processing, e.g. processing attemperatures ≧400° C., for example ≧450° C., ≧500° C., ≧550° C., ≧600°C., and on up to about 650° C., or in some cases to 700° C.

The surface modification layers 30, including the materials and bondingsurface heat treatments, as exemplified by the examples 2a, 2e, 3 a, 3b,4c, 4d, and 4e, above, may be used to provide the controlled bondingareas 40 between the carrier 10 and the thin sheet 20. Specifically,these surface modification layers may be formed within the perimeters 52of the arrays 50 either on the carrier 10 or on the thin sheet 20.Accordingly, when the article 2 is processed at high temperature duringdevice processing, there can be provided a controlled bond between thecarrier 10 and the thin sheet 20 within the areas bounded by perimeters52 whereby a separation force may separate (without catastrophic damageto the thin sheet or carrier) the thin sheet and carrier in this region,yet the thin sheet and carrier will not delaminate during processing,including ultrasonic processing. Additionally, because of the very smallthickness of the surface modification layer, i.e., less than 100nanometers, less than 40 nanometers, less than 10 nanometers, and insome instances about 2 nanometers, there is no effect on the wafer dueto CTE mismatch between the wafer and the surface modification layer (asthere is in the case of thicker adhesive layers, i.e., on the order of40-60 microns or more). Additionally, when there is a need to limitoutgassing between the thin sheet and carrier, the surface modificationlayer materials of examples 3b, 4c, and 4e may be used.

Then, during extraction of the interposers 56 (each having an array 50of vias 60) having perimeters 52, the portions of thin sheet 20 withinthe perimeters 52 may simply be separated from the carrier 10 afterprocessing and after separation of the thin sheet along perimeters 52.Alternatively, the thin sheet 20 (and alternatively both the thin sheet20 and the carrier 10) may be diced along lines 5, whereby a section ofthe thin sheet 20 larger than the interposer 56 perimeter 52 may beremoved from the carrier 10, or sections of the carrier 10 as in theevent that the carrier is diced together with the thin sheet 20. Becausethe surface modification layers control bonding energy to preventpermanent bonding of the thin sheet with the carrier, they may be usedfor processes wherein temperatures are ≧600° C. Of course, althoughthese surface modification layers may control bonding surface energyduring processing at temperatures ≧600° C., they may also be used toproduce a thin sheet and carrier combination that will withstandprocessing at lower temperatures for example ≧400° C. (for example ≧450°C., ≧500° C., ≧550° C.), and may be used in such lower temperatureapplications. Moreover, where the thermal processing of the article willnot exceed 400° C., surface modification layers as exemplified by theexamples 2c, 2d, 4b may also be used—in some instances, depending uponthe other process requirements—in this same manner to control bondingsurface energy. Moreover, as noted above, the surface modification layermaterials of examples 3b, 4c, and 4e, may be used in instances wereoutgassing between the thin sheet and carrier is a concern.

CONCLUSION

It should be emphasized that the above-described embodiments of thepresent invention, particularly any “preferred” embodiments, are merelypossible examples of implementations, merely set forth for a clearunderstanding of various principles of the invention. Many variationsand modifications may be made to the above-described embodiments of theinvention without departing substantially from the spirit and variousprinciples of the invention. All such modifications and variations areintended to be included herein within the scope of this disclosure andthe present invention and protected by the following claims.

For example, although the surface modification layer 30 of manyembodiments is shown and discussed as being formed on the carrier 10, itmay instead, or in addition, be formed on the thin sheet 20. That is,the materials as set forth in the examples 4 and 3 may be applied to thecarrier 10, to the thin sheet 20, or to both the carrier 10 and thinsheet 20 on faces that will be bonded together.

Further, although some surface modification layers 30 were described ascontrolling bonding strength so as to allow the thin sheet 20 to beremoved from the carrier 10 even after processing the article 2 attemperatures of 400° C., or of 600° C., of course it is possible toprocess the article 2 at lower temperatures than those of the specifictest the article passed and still achieve the same ability to remove thethin sheet 20 from the carrier 10 without damaging either the thin sheet20 or the carrier 10.

Still further, although the controlled bonding concepts have beendescribed herein as being used with a carrier and a thin sheet, incertain circumstances they are applicable to controlling bonding betweenthicker sheets of glass, ceramic, or glass ceramic, wherein it may bedesired to detach the sheets (or portions of them) from each other.

Further yet, although the controlled bonding concepts herein have beendescribed as being useful with glass carriers and glass thin sheets, thecarrier may be made of other materials, for example, ceramic, glassceramic, or metal. Similarly, the sheet controllably bonded to thecarrier may be made of other materials, for example, ceramic or glassceramic.

What is claimed is:
 1. An article, comprising: a carrier with a carrierbonding surface; a sheet with at least one via therein, the sheetfurther comprising a sheet bonding surface; a surface modificationlayer; the carrier bonding surface being bonded with the sheet bondingsurface with the surface modification layer therebetween, wherein thesurface modification layer is of such a character that at least one of:(i) after subjecting the article to a temperature cycle by heating in anchamber cycled from room temperature to 500° C. at a rate of 9.2° C. perminute, held at a temperature of 500° C. for 10 minutes, and then cooledat furnace rate to 300° C., and then removing the article from thechamber and allowing the article to cool to room temperature, thecarrier and sheet do not separate from one another if one is held andthe other subjected to the force of gravity, and the sheet may beseparated from the carrier without breaking the thinner one of thecarrier and the sheet into two or more pieces when separation isperformed at room temperature; and (ii) after subjecting the article toa temperature cycle by heating in an chamber cycled from roomtemperature to 400° C. at a rate of 9.2° C. per minute, held at atemperature of 400° C. for 10 minutes, and then cooled at furnace rateto 300° C., and then removing the article from the chamber and allowingthe article to cool to room temperature, the carrier and sheet do notseparate from one another if one is held and the other subjected to theforce of gravity, there is no outgassing from the surface modificationlayer according to test #2, and the sheet may be separated from thecarrier without breaking the thinner one of the carrier and the sheetinto two or more pieces when separation is performed at roomtemperature.
 2. The article of claim 1, wherein the sheet comprisessilicon, quartz, sapphire, ceramic, or glass.
 3. An article, comprising:a carrier with a carrier bonding surface; a wafer sheet comprising athickness ≦200 microns, the sheet further comprising a sheet bondingsurface, the sheet comprising silicon, quartz, or sapphire; a surfacemodification layer; the carrier bonding surface being bonded with thesheet bonding surface with the surface modification layer there between,wherein the surface modification layer is of such a character that atleast one of: (i) after subjecting the article to a temperature cycle byheating in an chamber cycled from room temperature to 500° C. at a rateof 9.2° C. per minute, held at a temperature of 500° C. for 10 minutes,and then cooled at furnace rate to 300° C., and then removing thearticle from the chamber and allowing the article to cool to roomtemperature, the carrier and sheet do not separate from one another ifone is held and the other subjected to the force of gravity, and thesheet may be separated from the carrier without breaking the thinner oneof the carrier and the sheet into two or more pieces when separation isperformed at room temperature; and (ii) after subjecting the article toa temperature cycle by heating in an chamber cycled from roomtemperature to 400° C. at a rate of 9.2° C. per minute, held at atemperature of 400° C. for 10 minutes, and then cooled at furnace rateto 300° C., and then removing the article from the chamber and allowingthe article to cool to room temperature, the carrier and sheet do notseparate from one another if one is held and the other subjected to theforce of gravity, there is no outgassing from the surface modificationlayer according to test #2, and the sheet may be separated from thecarrier without breaking the thinner one of the carrier and the sheetinto two or more pieces when separation is performed at roomtemperature.
 4. The article of claim 1, at least one via has a diameterof ≦150 microns and comprises electrically conductive material therein.5. The article of claim 1, the sheet comprising a device surfaceopposite the sheet bonding surface, the device surface comprising anarray of devices selected from the group consisting of: integratedcircuits; MEMS; CPU; microsensors; power semiconductors; light-emittingdiodes; photonic circuits; interposers; embedded passive devices; andmicrodevices fabricated on or from silicon, silicon-germanium, galliumarsenide, and gallium nitride.
 6. The article of claim 1, wherein thereis no outgassing from the surface modification layer during the heating,wherein outgassing from the surface modification layer is defined as atleast one of: (a) wherein the change in surface energy of the cover is≧15 mJ/m² at a test-limit temperature of 600° C. according to outgassingtest #1; and (b) wherein the change in % bubble area is ≧5 at a testlimit temperature of 600° C. according to outgassing test #2.
 7. Thearticle of claim 1, the surface modification layer comprises one of: a)a plasma polymerized fluoropolymer; and b) an aromatic silane.
 8. Amethod of making an interposer, comprising: obtaining a carrier with acarrier bonding surface; obtaining a sheet with at least one viatherein, the sheet further comprising a sheet bonding surface, whereinat least one of the carrier bonding surface and the sheet bondingsurface comprises a surface modification layer thereon; bonding thecarrier to the sheet with the bonding surfaces and the surfacemodification layer to form an article; subjecting the article tofront-end-of-line (FEOL) processing, wherein after FEOL processing thecarrier and sheet do not separate from one another if one is held andthe other subjected to the force of gravity; removing the sheet from thecarrier without breaking the thinner one of the carrier and the sheetinto two or more pieces.
 9. The method of claim 8, the sheet comprisessilicon, quartz, sapphire, ceramic, or glass.
 10. A method of processinga silicon wafer sheet, comprising: obtaining a carrier with a carrierbonding surface; obtaining a wafer sheet with a thickness ≦200 microns,the sheet comprising silicon, quartz, or sapphire, the sheet furthercomprising a sheet bonding surface, wherein at least one of the carrierbonding surface and the sheet bonding surface comprises a surfacemodification layer thereon; bonding the carrier to the sheet with thebonding surfaces and the surface modification layer to form an article;subjecting the article to front-end-of-line (FEOL) processing, whereinafter FEOL processing the carrier and sheet do not separate from oneanother if one is held and the other subjected to the force of gravity;removing the sheet from the carrier without breaking the thinner one ofthe carrier and the sheet into two or more pieces.
 11. The method ofclaim 8, wherein the FEOL processing comprises at least one of: (i)processing-chamber temperatures of from 500° C. to 700° C.; and (ii) atleast one of: DRIE (dry reactive ion etch); PVD; CVD TiN; PECVD SiO2;Electrolytic Cu Plating; Cu Annealing; Metrology; Cu CMP; Cu(H2O2+H2SO4)+Ti (DHF) Wet Etch; Sputter Adhesion Layer; Sputter SeedLayer; Lithography (Photoresist, expose, strip, etch Cu).
 12. The methodof claim 8, the at least one via has a diameter of ≦150 microns andcomprises electrically conductive material therein.
 13. The method ofclaim 8, the sheet comprising a device surface opposite the sheetbonding surface, the device surface comprising at least one of: (i) anarray of devices selected from the group consisting of: integratedcircuits; MEMS; CPU; microsensors; power semiconductors; light-emittingdiodes; photonic circuits; interposers; embedded passive devices; andmicrodevices fabricated on or from silicon, silicon-germanium, galliumarsenide, and gallium nitride; and (ii) at least one structure selectedfrom the group consisting of: solder bumps; metal posts; metal pillars;interconnection routings; interconnect lines; insulating oxide layers;and structures formed from a material selected from the group consistingof silicon, polysilicon, silicon dioxide, silicon (oxy)nitride, metal,low k dielectrics, polymer dielectrics, metal nitrides, and metalsilicides.
 14. The method of claim 8, wherein there is no outgassingfrom the surface modification layer during the heating, whereinoutgassing from the surface modification layer is defined as at leastone of: (a) wherein the change in surface energy of the cover is ≧15mJ/m² at a test-limit temperature of 600° C. according to outgassingtest #1; and (b) wherein the change in % bubble area is ≧5 at a testlimit temperature of 600° C. according to outgassing test #2.
 15. Themethod of claim 8, wherein the surface modification layer comprises oneof: a) a plasma polymerized fluoropolymer; and b) an aromatic silane.